Image display panel having a backlighting structure and a single-layer pixelated aray of reflective-type spectral filtering elements where between light is recycled for producing color images with enhanced brightness

ABSTRACT

An LCD panel employing a novel scheme of systemic light recycling. A single polarization state of light is transmitted from the backlighting structure to section of the LCD panel where both spatial intensity and spectral filtering of the transmitted polarized light simultaneously occurs on a subpixel basis. At each subpixel location, spectral bands of light not transmitted to the display surface during spectral filtering, are reflected without absorption back along the projection axis into the backlighting structure. At a subcomponent level within the LCD panel, spectral components of transmitted polarized light not used at any particular subpixel structure location are effectively reflected either directly or indirectly back into the backlighting structure.

RELATED CASES

This Application is a Continuation-in-Part of: application Ser. No.08/322,219 entitled “BACKLIGHTING CONSTRUCTION FOR USE IN COMPUTER-BASEDDISPLAY SYSTEMS HAVING DIRECT AND PROJECTION VIEWING MODES OF OPERATION”filed Oct. 13, 1994; which is now U.S. Letters Pat. No. 5,801,793; whichis a Continuation-in-Part of application Ser. No. 08/230,779 entitled“ELECTRO-OPTICAL BACKLIGHTING PANEL FOR USE IN COMPUTER-BASED DISPLAYSYSTEMS AND PORTABLE LIGHT PROJECTION DEVICE FOR USE THEREWITH”, filedApr. 21, 1994; now U.S. Letters Pat. No. 5/828,427; which is aContinuation-in-Part of application Ser. No. 08/126,077 entitled “METHODAND APPARATUS FOR RECORDING AND DISPLAYING SPATIALLY-MULTIPLEXED IMAGESOF 3-D OBJECTS FOR STEREOSCOPIC VIEWING THEREOF” filed Sep. 23, 1993,now U.S. Letters Pat. 5,537,144; which is a Continuation of applicationSer. No. 07/536,190 filed Jun. 11, 1990, now abandoned. These copendingApplications are commonly owned by Reveo, Inc. of Hawthorne, N.Y., andeach such Application is hereby incorporated herein by reference in itsentirety, as if fully set forth herein.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a high-brightness color liquid crystaldisplay (LCD) panel employing non-absorptive spectral filtering andlight recycling among neighboring subpixels, and also to methods andapparatus for manufacturing the same.

2. Brief Description of the Prior Art

Without question, there is a great need for flat display panels capableof displaying video imagery in both direct and projection modes ofviewing. Examples of equipment requiring such display structures fordirect viewing include notebook computers, laptop computers, and palmtopcomputers, and equipment requiring such display structures forprojection viewing include LCD projection panels and LCD imageprojectors.

In general, prior art color LCD display panels have essentially the samebasic construction in that each comprises the following basiccomponents, namely: a backlighting structure for producing a plane ofuniform intensity backlighting; an electrically-addressable array ofspatial-intensity modulating elements for modulating the spatialintensity of the plane of backlight transmitted therethrough; and anarray of color filtering elements in registration with the array ofspatial-intensity modulating elements, for spectral filtering theintensity modulated light rays transmitted therethrough, to form a colorimage for either direct or projection viewing. Examples of such priorart LCD panel systems are described in “A Systems Approach to ColorFilters for Flat-Panel Displays” by J. Hunninghake, et al, published inSID 94 DIGEST (pages 407-410).

In color LCD panel design, the goal is to maximize the percentage oflight transmitted from the backlighting structure through the colorfiltering array. However, using prior art design techniques, it has beenimpossible to achieve this design goal due to significant losses inlight transmission caused by the following factors, namely: absorptionof light energy due to absorption-type polarizers used in the LCDpanels; absorption of light reflected off thin-film transistors (TFTs)and wiring of the pixelated spatial intensity modulation arrays used inthe LCD panels; absorption of light by pigments used in the spectralfilters of the LCD panels; absorption of light energy by theblack-matrix used to spatially separate the subpixel filters in the LCDpanel in order to enhance image contrast; and Fresnel losses due to themismatching of refractive indices between layers within the LCD panels.As a result of such design factors, the light transmission efficiency ofprior art color LCD panels is typically no more than 5%. Consequently,up to 95% of the light produced by the backlighting structure isconverted into heat across the LCD panel. Thus, it is impossible toproduce high brightness images from prior art color LCD panels used ineither direct or projection display systems without using ultra-highintensity backlighting sources which require high power supplies, andproduce great amounts of heat necessitating cooling measures and thelike.

In response to the drawbacks of prior art color LCD panel design,several alternative approaches have been proposed in order to improvethe light transmission efficiency of the panel and thus the brightnessof images produced therefrom. For example, U.S. Pat. No. 5,325,218 toWillett et al. discloses an LCD panel which uses tuned cholestericliquid crystal (CLC) polarizers to replace absorptive dyed (neutral ordichroic) polarizers of prior art LCD panels to improve color purity,and a partial (i.e. local) light recycling scheme in order to improvethe brightness of the LCD panel. U.S. Pat. No. 5,418,631 to Tedesco alsodiscloses an LCD panel which uses a holographic diffuser for directinglight out from the light guiding panel of the backlighting panelingstructure, and CLC polarizers for locally recycling light diffused bythe holographic diffuser in order to improve the brightness of the LCDpanel. However, such prior art color LCD panel designs are not withoutshortcomings and drawbacks.

In particular, notwithstanding the use of non-absorptive CLC filters andlocalized light recycling principles, prior art LCD panels continue torequire at least one light absorptive layer along the optical pathextending from the backlighting structure to the viewer (i.e. along thelight projection axis). Consequently, prior art LCD panels have very lowlight transmission efficiencies. Thus the production of high brightnesscolor images from prior art LCD panels has required high-intensitybacklighting sources which consume great amounts of electrical power andproduce high quantities of heat, and necessitate the use of fans andother cooling measures to maintain the temperature of both the LCD paneland the lamp(s) in the backlight structure within safe operatinglimits.s

Thus, there is a great need in the art for an improved color LCD panelwhich is capable of producing high brightness color images without theshortcomings and drawbacks of the prior art LCD panel devices.

OBJECTS AND SUMMARY OF THE PRESENT INVENTION

Accordingly, a primary object of the present invention is to provide animproved color LCD panel capable of producing high brightness colorimages, while avoiding the shortcomings and drawbacks of prior arttechniques.

Another object of the present invention is to provide such a color LCDpanel, in which the spatial-intensity modulation and spectral filteringfunctions associated with each subpixel structure of the LCD panel arerealized at a different location along the x and y axes thereof.

Another object of the present invention is to provide such a color LCDpanel, in which the spatial-intensity modulation and spectral (i.e.color) filtering functions associated with each and every subpixelstructure of the LCD panel are carried out using systemic lightrecycling principles which virtually eliminate any and all absorption ordissipation of the spectral energy produced from the backlightingstructure during color image production.

Another object of the present invention is to provide such a color LCDpanel, in which a single polarization state of light is transmitted fromthe backlighting structure to the section of the LCD panel along theprojection axis thereof, to those structure or subpanels where bothspatial intensity and spectral filtering of the transmitted polarizedlight simultaneously occurs on a subpixel basis in a functionallyintegrated manner. At each subpixel location, spectral bands of lightwhich are not transmitted to the display surface during spectralfiltering, are reflected without absorption back along the projectionaxis into the backlighting structure where the polarized light isrecycled with light energy being generated therewith. The recycledspectral components are then retransmitted from the backlightingstructure into section of the LCD panel where spatial intensitymodulation and spectral filtering of the retransmitted polarized lightsimultaneously reoccurs on a subpixel basis in a functionally integratedmanner.

Another object of the present invention is to provide such a color LCDpanel, in which the spatial-intensity modulation and spectral filteringfunctions associated with each and every subpixel structure of the LCDpanel are carried out using the polarization/wavelength dependenttransmission and reflection properties of CLC-based filters.

Another object of the present invention is to provide such a color LCDpanel having a multi-layer construction with multiple opticalinterfaces, at which non-absorbing broad-band and pass-band (i.e. tuned)polarizing reflective panels are used to carryout systemic lightrecycling within the LCD panel such that light produced from thebacklighting structure is transmitted through the LCD panel with a lighttransmission efficiency of at least %90.

A further object of the present invention is to provide a novel LCDpanel, in which both non-absorbing broad-band and pass-band (i.e. tuned)polarizer filters are used to avoid absorbing or dissipating any of thespectral energy produced from the backlighting structure during imageproduction in order that high-brightness images can be produced usinglow-intensity backlighting structures.

Another object of the present invention is to provide such a color LCDpanel, in which an array of pass-band CLC polarizing filter elements andan array of electrically-controlled liquid crystal elements are disposedbetween a pair of broad-band CLC polarizing filter panels used torealize the LCD panel.

Another object of the present invention is to provide such a color LCDpanel, in which the spectral components of light produced from thebacklighting structure are recycled (i) between the spectral filteringarray and the backlighting structure, (ii) within the backlightingstructure itself, and (iii) among adjacent subpixels within the LCDpanel in order to improve the overall light transmission efficiency ofthe LCD panel.

Another object of the present invention is to provide such a color LCDpanel, in which the array of liquid crystal elements can be realizedusing an array of electrically-controlled birefringent (ECB) elementswhich rotate the linear polarization state of the transmitted light, orinvert the polarization state of circularly polarized light beingtransmitted through the LCD panel.

Another object of the present invention is to provide such a color LCDpanel, in which the backlighting structure thereof can be realized usinga light guiding panel based on the principle of total internalreflection, a holographic diffuser based on the principle of refractiveindex matching and first order diffraction, or other suitable edge-litbacklighting structure which follows in general accordance with thephysical principles of the present invention.

These and other objects of the present invention will become apparenthereinafter and in the Claims to Invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the Objects of the PresentInvention, the following Detailed Description of the IllustrativeEmbodiments should be read in conjunction with the accompanyingdrawings, wherein:

FIG. 1A is a schematic representation of a direct-view type imagedisplay system in which the LCD panel of the present invention isemployed;

FIG. 1B is a schematic representation of a projection-view type imagedisplay system in which the LCD panel of the present invention isemployed;

FIG. 2 is an exploded schematic diagram of the first generalized LCDpanel construction of the present invention, comprising (i) itsbacklighting structure realized by a quasi-specular reflector, a lightguiding panel, a pair of edge-illuminating light sources, and broad-bandpolarizing reflective panel, (ii) its spatial-intensity modulating arrayrealized as an array of electronically-controlled polarization directionrotating elements, and (iii) its array of spectral filtering elementsrealized as an array of pass-band polarizing reflective elements and abroad-band linearly polarizing reflective panel;

FIG. 2A is a perspective, partially broken away view of a portion of theLCD panel of FIG. 2, showing the electronically-controlled polarizationrotating elements associated with a pixel structure thereof;

FIG. 3A1 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a first particularembodiment of the LCD panel shown in FIG. 2, wherein thespatial-intensity modulating elements of the LCD panel are realizedusing linear-type polarization rotating elements, and the pixel driversignals provided thereto are selected to produce “dark” output levels ateach of the RGB subpixels of the exemplary pixel structure;

FIG. 3A2 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within the first particularembodiment of the LCD panel shown in FIG. 2, wherein thespatial-intensity modulating elements of the LCD panel are realizedusing linear-polarization rotating elements, and the pixel driversignals provided thereto are selected to produce “bright” output levelsat each of the RGB subpixels of the exemplary pixel structure;

FIG. 3B is a schematic representation graphically illustrating thereflection characteristics of the first broad-band linear polarizing(LP1) reflective panel of the LCD panel of FIGS. 3A1 and 3A2, indicatinghow such a broad-band linear polarizing panel responds to incidentilluminating having linear polarization state LP1;

FIG. 3C is a schematic representation graphically illustrating thereflection characteristics of the second broad-band linear polarizing(LP1) reflective panel of the LCD panel of FIGS. 3A1 and 3A2, indicatinghow such a broad-band linear polarizing panel responds to incidentilluminating having linear polarization state LP1;

FIG. 3D is a schematic representation graphically illustrating thereflection characteristics of the pass-band linear polarizing (LP2)reflective filter element associated with each “blue” subpixel of theLCD panel of FIGS. 3A1 and 3A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving linear polarization state LP2;

FIG. 3E is a schematic representation graphically illustrating thereflection characteristics of the pass-band linear polarizing (LP2)reflective filter element associated with each “green” subpixel of theLCD panel of FIGS. 3A1 and 3A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving linear polarization state LP2;

FIG. 3F is a schematic representation graphically illustrating thereflection characteristics of the pass-band linear polarizing (LP2)reflective filter element associated with each “red” subpixel of the LCDpanel of FIGS. 3A1 and 3A2, indicating how such a non-absorbing spectralfilter element responds to incident broad-band illumination havinglinear polarization state LP2;

FIG. 4A1 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a second particularembodiment of the LCD panel shown in FIG. 2, wherein thespatial-intensity modulating elements of the LCD panel are realizedusing circular-type polarization rotating elements, and the pixel driversignals provided thereto are selected to produce “dark” output levels ateach of the RGB subpixels of the exemplary pixel structure;

FIG. 4A2 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within the second particularembodiment of the LCD panel shown in FIG. 2, wherein thespatial-intensity modulating elements of the LCD panel are realizedusing circular-type polarization rotating elements, and the pixel driversignals provided thereto are selected to produce “bright” output levelsat each of the RGB subpixels of the exemplary pixel structure;

FIG. 4B is a schematic representation graphically illustrating thereflection characteristics of the broad-band left-handed circularlypolarizing (LHCP) reflective panel of the LCD panel of FIGS. 4A1 and4A2, indicating how such a broad-band circularly polarizing panelresponds to incident illuminating having the circular polarization stateLHCP;

FIG. 4C is a schematic representation graphically illustrating thereflection characteristics of the broad-band right handed circularlypolarizing (RHCP) reflective panel of the LCD panel of FIGS. 2, 4A1 and4A2, indicating how such a broad-band circularly polarizing panelresponds to incident illuminating having circular polarization stateRHCP;

FIG. 4D is a schematic representation graphically illustrating thereflection characteristics of the pass-band left-handed circularlypolarizing (LHCP) reflective filter element associated with each “blue”subpixel of the LCD panel of FIGS. 4A1 and 4A2, indicating how such anon-absorbing spectral filter element responds to incident broad-bandillumination having the left-handed circular polarization state LHCP;

FIG. 4E is a schematic representation graphically illustrating thereflection characteristics of the pass-band left handed circularlypolarizing (LHCP) reflective filter element associated with each “green”subpixel of the LCD panel of FIGS. 4A1 and 4A2, indicating how such anon-absorbing spectral filter element responds to incident broad-bandillumination having the left handed circular polarization state LHCP;

FIG. 4F is a schematic representation graphically illustrating thereflection characteristics of the pass-band left handed circularlypolarizing (LHCP) reflective filter element associated with each “red”subpixel of the LCD panel of FIGS. 4A1 and 4A2, indicating how such anon-absorbing spectral filter element responds to incident broad-bandillumination having the left handed circular polarization state LHCP;

FIG. 5 is schematic diagram of apparatus for use in manufacturing theLCD panel of the present invention;

FIG. 6 is schematic representation of an empirically determined functiongraphically illustrating the characteristic wavelength of CLC materialused to make the pass-band circularly polarizing filter array of theillustrative embodiments, plotted as a function of the temperature atwhich the CLC material is exposed to ultra-violet radiation duringmanufacture;

FIGS. 7A through 7C, taken together, provide a flow chart illustratingthe steps undertaken during the preferred method of manufacturing theLCD panel;

FIG. 8 is an exploded schematic diagram of the second generalized LCDpanel construction of the present invention comprising (i) itsbacklighting structure realized by a quasi-specular reflector, a lightguiding panel, a pair of edge-illuminating light sources, and broad-bandpolarizing reflective panel, (ii) its array of spectral filteringelements realized as an array of pass-band polarizing reflectiveelements; and (iii) its spatial-intensity modulating array realized asan array of electronically-controlled polarization rotating elements anda broad-band polarizing reflective panel;

FIG. 8A is a perspective, partially broken away view of a portion of theLCD panel shown in FIG. 8, showing the electronically-controlledpolarization rotating elements associated with a pixel structurethereof;

FIG. 9A1 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within the LCD panel of FIG. 7,wherein the spatial-intensity modulating elements of the LCD panel arerealized using linear-type polarization rotating elements, and the pixeldriver signals provided thereto are selected to produce “bright” outputlevels at each of the RGB subpixels of the exemplary pixel structure;

FIG. 9A2 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within the particular embodiment ofthe LCD panel shown in FIG. 8, wherein the spatial-intensity modulatingelements of the LCD panel are realized using linear-type polarizationrotating elements, and the pixel driver signals provided thereto areselected to produce “dark” output levels at each of the RGB subpixels ofthe exemplary pixel structure;

FIG. 9B is a schematic representation graphically illustrating thereflection characteristics of the broad-band linear polarizing (LP1)reflective panel of the LCD panel of FIGS. 9A1 and 9A2, indicating howsuch a broad-band linear polarizing panel responds to incidentilluminating having linear polarization state LP1;

FIG. 9C is a schematic representation graphically illustrating thereflection characteristics of the absorptive broad-band linearpolarizing (LP2) panel of the LCD panel of FIGS. 9A1 and 9A2, indicatinghow such a broad-band linear polarizing panel responds to incidentilluminating having linear polarization state LP2;

FIG. 9D is a schematic representation graphically illustrating thereflection characteristics of the pass-band linear polarizing (LP2)reflective filter element associated with each “blue” subpixel of theLCD panel of FIGS. 9A1 and 9A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving linear polarization state LP2;

FIG. 9E is a schematic representation graphically illustrating thereflection characteristics of the pass-band linear polarizing (LP2)reflective filter element associated with each “green” subpixel of theLCD panel of FIGS. 9A1 and 9A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving linear polarization state LP2;

FIG. 9F is a schematic representation graphically illustrating thereflection characteristics of the pass-band linear polarizing (LP2)reflective filter element associated with each “red” subpixel of the LCDpanel of FIGS. 9A1 and 9A2, indicating how such a non-absorbing spectralfilter element responds to incident broad-band illumination havinglinear polarization state LP2;

FIG. 10A1 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a second particularembodiment of the LCD panel of FIG. 8, wherein the spatial-intensitymodulating elements of the LCD panel are realized using circular-typepolarization rotating elements, and the pixel driver signals providedthereto are selected to produce “bright” output levels at each of theRGB subpixels of the exemplary pixel structure;

FIG. 10A2 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within the second particularembodiment of the LCD panel of FIGS. 8, wherein the spatial-intensitymodulating elements of the LCD panel are realized using circular-typepolarization rotating elements, and the pixel driver signals providedthereto are selected to produce “dark” output levels at each of the RGBsubpixels of the exemplary pixel structure;

FIG. 10B is a schematic representation graphically illustrating thereflection characteristics of the broad-band circularly polarizing(LHCP) reflective panel of the LCD panel of FIGS. 10A1 and 10A2,indicating how such a broad-band circularly polarizing panel responds toincident illuminating having circular polarization state LHCP;

FIG. 10C is a schematic representation graphically illustrating thereflection characteristics of the broad-band circularly polarizing(RHCP) reflective panel of the LCD panel of FIGS. 10A1 and 10A2,indicating how such a broad-band circularly polarizing panel responds toincident illuminating having circular polarization state RHCP;

FIG. 10D is a schematic representation graphically illustrating thereflection characteristics of the pass-band circularly polarizing (RHCP)reflective filter element associated with each “blue” subpixel of theLCD panel of FIGS. 10A1 and 10A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving circular polarization state RHCP;

FIG. 10E is a schematic representation graphically illustrating thereflection characteristics of the pass-band circularly polarizing (RHCP)reflective filter element associated with each “green” subpixel of theLCD panel of FIGS. 10A1 and 10A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving circular polarization state RHCP;

FIG. 10F is a schematic representation graphically illustrating thereflection characteristics of the pass-band circular polarizing (RHCP)reflective filter element associated with each “red” subpixel of the LCDpanel of FIGS. 10A1 and 10A2, indicating how such a non-absorbingspectral filter element responds to incident broad-band illuminationhaving circular polarization state RHCP;

FIG. 11 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a third embodiment of theLCD panel shown in FIG. 2, wherein the spatial-intensity modulatingelements of the LCD panel are realized using linear-type polarizationrotating elements, the pixel driver signals provided thereto areselected to produce “dark” output levels the red and blue subpixels ofthe exemplary pixel structure and a “bright” output level at the greensubpixel level, and broad-band absorptive linear polarizer is used inconjunction with each broad-band polarizing reflective panel in the LCDpanel in order to provide improved image contrast in images displayedtherefrom;

FIG. 12 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a fourth embodiment of theLCD panel shown in FIG. 2, wherein the spatial-intensity modulatingelements of the LCD panel are realized using circular-type polarizationrotating elements, the pixel driver signals provided thereto areselected to produce “dark” output levels at the red and blue subpixelsof the exemplary pixel structure and a “bright” output level at thegreen subpixel level, and a broad-band absorptive linear polarizer isused in conjunction with each broad-band polarizing reflective panel inthe LCD panel in order to provide improved image contrast in the imagesdisplayed therefrom;

FIG. 13 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a third embodiment of theLCD panel shown in FIG. 8, wherein the spatial-intensity modulatingelements of the LCD panel are realized using linear-type polarizationrotating elements, the pixel driver signals provided thereto areselected to produce “bright” output levels the red and blue subpixels ofthe exemplary pixel structure and a “dark” output level at the greensubpixel level, and a broad-band absorptive linear polarizer is used inconjunction with each broad-band polarizing reflective panel in the LCDpanel in order to provide improved image contrast in the imagesdisplayed therefrom;

FIG. 14 is a schematic representation of an exploded, cross-sectionalview of an exemplary pixel structure within a fourth embodiment of theLCD panel shown in FIG. 8, wherein the spatial-intensity modulatingelements of the LCD panel are realized using circular-type polarizationrotating elements, the pixel driver signals provided thereto areselected to produce “bright” output levels the red and blue subpixels ofthe exemplary pixel structure and a “dark” output level at the greensubpixel level, and a broad-band absorptive linear polarizer is used inconjunction with each broad-band polarizing reflective panel in the LCDpanel in order to provide improved image contrast in the imagesdisplayed therefrom; and

FIG. 15 is a schematic representation of a portable color imageprojection system in the form of a laptop computer, wherein a pluralityof conventional backlighting structures are cascaded together andmounted to the rear portion of an LCD panel according to the presentinvention in order to provide an LCD panel assembly that can be mountedwithin the display portion of the system housing and project brightimages onto a remote surface without the use of an external light sourceor a rear opening in the display portion of the housing, for projectinglight therethrough during its projection-viewing mode of operation.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS OF THE PRESENTINVENTION

Referring now to the figures in the accompanying Drawings, theillustrative embodiments of the present invention will now be describedin detail, wherein like structures and elements shown within the figuresare indicated with like reference numerals.

Overview of the LCD Image Display System of Present Invention

As shown in FIG. 1A, the LCD panel of the present invention is shown aspart of a direct-view type color image display system 1 which is capableof supporting displaying high-resolution color images. During operation,the LCD panel 2 is actively driven by pixel driver circuitry 3 inresponse to color image data sets produced from a host system 4 whichcan be a computer-graphics board (subsystem), a video source (e.g. VCR),camera, or like system. The function of the LCD panel 2 is to spatialintensity modulate and spectrally filter on a subpixel basis the lightemitted from an edge-illuminated backlighting structure 2A which may berealized in a variety of ways. The optically processed pattern of lightforms color images at the surface of the LCD panel for direct viewing.

As shown in FIG. 1B, the LCD panel of the present invention 2′ is shownas part of a projection-view type color image display system 1′ which iscapable of supporting displaying high-resolution color images. Duringoperation, the LCD panel 2′ is actively driven by pixel driver circuitry3 in response to color image data sets produced from host system 4 whichcan be a computer-graphics board (subsystem), a video source (e.g. VCR),camera, or like system. The function of light source 5 is to produce andproject a beam of light through the entire extent of the LCD panel. Thefunction of the LCD panel is to spatial intensity modulate andspectrally filter the projected light on a subpixel basis. The opticallyprocessed pattern of light forms color images at the surface of the LCDpanel which are then projected by projection optics 6 onto a remotedisplay surface (e.g. screen or wall) for projection viewing.

The systems shown in FIGS. 1A and 1B are each designed to supportmonoscopic viewing of color images representative of 2-D and/or 3-Dgeometry. However, these image display systems can be readily adapted tosupport stereoscopic viewing of 3-D objects and scenery of either a realand/or synthetic nature. One way of providing such viewing capabliltiesis to mount (i.e. laminate) a micropolarization panel upon the displaysurface of the LCD panels 2 and 2′ in order to display micropolarizedspatially multiplexed images (SMIs) of 3-D objects and scenery, forviewing through electrically-passive polarizing eyeglasses, as disclosedin Applicant's International Patent Application No. PCT/US97/03985, nowpublished as WIPO Publication No. WO 97/34184.

In FIG. 2, the subcomponent structure of the first generalizedembodiment of the LCD panel hereof is shown in great clarity. As shown,the first generalized embodiment of the LCD panel 2 comprises: abacklighting structure 7 including a quasi-diffusive reflector 7A, forproducing a plane of broad-band light having a substantially uniformlight intensity over the x and y coordinate axes thereof; a broad-bandpolarizing reflective panel 8; a pixelated array of polarizationdirection rotating elements 9 for spatial intensity modulation of lightproduced from the backlighting structure; a pixelated array ofpolarizing reflective spectral filter elements 10, for spectralfiltering of light produced from the backlighting structure; and abroad-band polarizing reflective panel 11 for cooperative operation withthe pixelated array of polarization direction rotating elements 9 andthe pixelated array of polarizing reflective spectral filter elements10.

In order to produce high-resolution color images, the spatial period ofthe pixelated arrays 9 and 10 is selected to be relatively small inrelation to the overall length and height dimensions of the LCD panel.In a conventional manner, each pixel structure in the LCD panel iscomprised of a red subpixel 13A, a green subpixel 13B and blue subpixel13C, as illustrated in FIG. 2A. As shown therein, each red subpixelstructure 13A comprises a red-band polarizing reflective spectralfiltering element 10A which is spatially registered with a firstpolarization direction rotating element 9A. Each green subpixelstructure 13B comprises a green-band polarizing reflective spectralfiltering element 10B spatially registered with a second polarizationdirection rotating element 9B. Each blue subpixel element 13C comprisesa blue-band polarizing reflective spectral filtering element 10Cspatially registered with a third polarization direction rotatingelement 9C. The output intensity (i.e. brightness or darkness level) ofeach red subpixel structure is controlled by applying pulse-widthmodulated voltage signal V_(R) to the electrodes of itselectrically-controlled spatially intensity modulating element. Theoutput intensity of each green subpixel structure is controlled byapplying pulse-width modulated voltage signal V_(G) to the electrodes ofits electrically-controlled spatially intensity modulating element. Theoutput intensity of each blue subpixel structure is controlled byproviding pulse-width modulated voltage signal V_(B) applied to theelectrodes of its electrically-controlled spatially intensity modulatingelement. By simply controlling the width of the above-described voltagesV_(R), V_(G), V_(B), the grey-scale intensity (i.e. brightness) level ofeach subpixel structure can be controlled in a manner well known in theLCD panel art.

Overview of the First Generalized Embodiment of the LCD PanelConstruction of the Present Invention

In the first generalized LCD panel construction shown in FIG. 2,spectral filtering occurs after spatial intensity modulation. In thefirst illustrative embodiment of this LCD panel construction shown inFIGS. 3A1 and 3A2, linear polarization techniques are used to carry outthe spatial intensity modulation and spectral filtering functionsemployed therein. In the second illustrative embodiment of this LCDpanel construction shown in FIGS. 4A1 and 4A2, circular polarizationtechniques are used to carry out the spatial intensity modulation andspectral filtering functions employed therein. In each such illustrativeembodiment, modifications will be made among the various components ofthe LCD panel shown in FIG. 2. Details regarding such modifications willbe described hereinafter.

First Illustrative Embodiment Of the LCD Panel Construction of FIG. 2

In the illustrative embodiments shown in FIGS. 3A1 and 3A2, thebacklighting structure 7 is realized by quasi-diffusive reflector 7A, alight guiding panel 7B, a pair of edge-illuminating light sources 7C1and 7C2, and a pair of focusing mirrors 7D1 and 7D2, respectively, forcoupling light produced by light sources 7C1 and 7C2 into the edges oflight guiding panel 7B. Preferably, the light guiding panel 7B is madefrom an optically transparent substrate such as Plexiglass® acrylic, andlight sources 7C1 and 7C2 are realized by a pair of miniaturefluorescent tubes which produce unpolarized light.

During backlight operation, light produced by sources 7C1 and 7C2 iscoupled with the help of reflectors 7D1 and 7D2 into the edges of thelight guiding panel 7B where it is totally internally reflected in aconventional manner. In the illustrative embodiment, the front surfaceof the light guiding panel 7B bears very fine pits in order to createoptical conditions at the surface thereof which destroys conditions fortotal internal reflection and allows light to leak out in the directionof the array of spatial intensity modulating elements. Understandably,there are many alternative techniques for producing a plane ofunpolarized light that can be used in the construction of any particularembodiment of the LCD panel of the present invention.

For purposes of illustration only, the spectral filtering functionrealized within each LCD panel of the illustrative embodiments is basedon the RGB (red, green, blue) additive primary color system.Alternatively, however, the spectral filtering function within each LCDpanel may be based on the CMY (cyan, magenta, yellow) subtractiveprimary color system.

In the illustrative embodiments of the LCD panel hereof, the emissionspectrum of the light source within the backlighting panel is assumed tobe “white”, and the spectral filtering function of the LCD panel isbased on the RGB color system. Thus, each polarizing reflective spectralfilter element 10A, 10B, 10C is designed to have “pass-band”characteristics so that all of the spectral content of the red, greenand blue bands of the light source are used to produce color images fordisplay. In such illustrative embodiments, each polarizing reflectivespectral filter element 10A, 10B and 10C is realized as a “pass-band”polarizing reflective spectral filter element.

However, in other embodiments of the LCD panel hereof, the light sourcewithin its backlighting structure may emit a “narrow-band” spectra overthe red, green and blue bands of the optical spectrum. In suchalternative embodiments of the LCD panel, the pixelated array ofpolarizing reflective spectral filter elements can be tailored tooverlap the RGB emission spectra. In such alternative embodiments, eachpolarizing reflective spectral filter element 10A, 10B and 10C can berealized as a “narrow-band” polarizing reflective spectral filterelement.

In the illustrative embodiment of FIGS. 3A1 and 3A2, the broad-bandlinear polarizing reflective panel 8′ has a characteristic linearpolarization state LP1 which serves as a polarization reference.Similarly, broad-band linear polarizing reflective panel 11′ has acharacteristic linear polarization state LP1. The reflectioncharacteristics of the broad-band linearly polarizing reflective panel8′ are graphically illustrated in FIG. 3B for incident light havinglinear polarization state LP1, whereas the reflection characteristics ofthe broad-band linearly polarizing reflective panel 11′ are graphicallyillustrated in FIG. 3C for incident light having linear polarizationstate LP1. For incident light having orthogonal linear polarizationstate LP2, the broad-band transmission characteristics for these panelsare substantially uniform for all wavelengths over the optical band.

In the illustrative embodiments of the LCD panel hereof, each“pass-band” polarizing reflective spectral filter element in pixelatedarray 10′ and broad-band polarizing reflective panels 8′ and 11′ arerealized using cholesteric liquid crystal (CLC) material of the typedisclosed in U.S. Letters Pat. No. 5,691,789, incorporated herein byreference in its entirety. The polarizing reflective properties of suchCLC material is described in detail in Applicant's U.S. Pat. No.5,221,982, incorporated herein by reference.

A preferred method of making the broad-band circularly polarizingreflective panels 8′ and 11′ is disclosed in great detail in U.S.Letters Pat. No. 5,691,789, supra. An alternative method of makingbroad-band linearly polarizing reflective panels 8′ and 11′ is disclosedin EPO Application No. 94200026.6 entitled “Cholesteric Polarizer andManufacture Thereof”.

In the illustrative embodiment of FIGS. 3A1 and 3A2, the polarizationrotating array 9 is realized as an array of electronically-controlledlinear polarization rotating elements 9′ for rotating the linearlypolarized electric field along LP1 to the LP2 polarization direction asthe light rays are transmitted through the spatially correspondingpixels in the LCD panel. In the illustrative embodiment of FIGS. 3A1 and3A2, each electronically-controlled linear polarization rotating elementcan be realized as a twisted nematic (TN) liquid crystal cell,super-twisted nematic (STN) liquid crystal cell, or ferro-electric cell,whose operation is by controlled by a control voltage well known in theart. To construct the linear polarization rotating elements, thin filmtransistors (TFTs) can be used to create the necessary voltages across alayer of liquid crystal material to achieve alignment of the liquidcrystal molecules and thus cause the corresponding element to not rotatethe polarization direction of transmitted light passing therethrough. Inits electrically-inactive state (i.e. no voltage is applied), theelectric field intensity of light exiting from the cell is substantiallyzero and thus a “dark” subpixel level is produced. In itselectrically-active state (i.e. the threshold voltage V_(T) is applied),the electric field intensity of light exiting from the cell issubstantially non-zero and thus a “bright” subpixel level is produced.

In the illustrative embodiment of FIG. 3A1 and 3A2, the pixelated arrayof spectral filtering elements 10 is realized as an array of pass-bandlinear polarizing reflective elements 10′ formed within a single plane.Broad-band linearly polarizing reflective panel 11′ is laminated to thepixelated array of spectral filtering elements 10. As indicated in FIGS.3A1 and 3A2, each pass-band linear polarizing reflective element in thepixelated pass-band linear polarizing panel 10′ has a LP2 characteristicpolarization state, whereas the broad-band linear polarizing reflectivepanel has an LP1 characteristic polarization state.

As shown in FIG. 3D, each pass-band polarizing reflective elementassociated with a “blue” subpixel in the pixelated pass-band linearpolarizing panel 10′ is particularly designed to reflect nearly 100% allspectral components having the LP2 characteristic polarization state anda wavelength within the green reflective band Δλ_(G) or the redreflective band Δλ_(R), whereas all spectral components having the LP2characteristic polarization state or a wavelength within the bluereflective band Δλ_(B) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The manner in which the pass-bandpolarizing reflective element 10C′ associated with each “blue” subpixelis “tuned” will be described hereinafter with reference to the method ofLCD panel fabrication illustrated in FIGS. 5, 6, 7A through 7C.

As shown in FIG. 3E, each pass-band polarizing reflective elementassociated with a “green” subpixel in the pixelated pass-band linearpolarizing panel 10′ is particularly designed to reflect nearly 100% allspectral components having the LP2 characteristic polarization state anda wavelength within the red reflective band Δλ_(R) or the bluereflective band Δλ_(B), whereas all spectral components having the LP2characteristic polarization state or a wavelength within the greenreflective band Δλ_(G) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The manner in which the pass-bandpolarizing reflective element 10B′ associated with each “green” subpixelis “tuned” will be described hereinafter with reference to the method ofLCD panel fabrication illustrated in FIGS. 5, 6, 7A through 7C.

As shown in FIG. 3F, each pass-band polarizing reflective elementassociated with a “red” subpixel in the pixelated pass-band linearpolarizing panel 10′ is particularly designed to reflect nearly 100% allspectral components having the LP2 characteristic polarization state anda wavelength within the green reflective band Δλ_(G) or the bluereflective band Δλ_(B), whereas all spectral components having the LP2characteristic polarization state or a wavelength within the redreflective band Δλ_(R) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The manner in which the pass-bandpolarizing reflective element 10A′ associated with each “red” subpixelis “tuned” will be described hereinafter with reference to the method ofLCD panel fabrication illustrated in FIGS. 5, 6, 7A through 7C.

Second Illustrative Embodiment Of the LCD Panel Construction of FIG. 2

In the illustrative embodiment of the LCD panel shown in FIGS. 4A1 and4A2, the backlighting structure 7 is realized in a manner describedabove. The broad-band linear polarizing reflective panel 8″ has acharacteristic circular polarization state LHCP (i.e. Left Hand CircularPolarization) which serves as a polarization reference. Broad-bandcircular polarizing reflective panel 11″ has a characteristic circularpolarization state RHCP (i.e. Right Hand Circular Polarization) which isorthogonal to LHCP. A preferred method of making the broad-bandcircularly polarizing reflective panels 8′″ and 11′″ is disclosed ingreat detail in U.S. Letters Pat. No. 5,691,789, supra. An alternativemethod of making broad-band circularly polarizing reflective panels 8″and 11″ is disclosed in EPO Application No. 94200026.6 entitled“Cholesteric Polarizer and Manufacture Thereof”. The reflectioncharacteristics of the broad-band circularly polarizing reflective panel8″ are graphically illustrated in FIG. 4B for incident light havingcircular polarization state LHCP, whereas the reflection characteristicsof the broad-band circularly polarizing reflective panel 11″ aregraphically illustrated in FIG. 4C for incident light having circularpolarization state RHCP.

In the illustrative embodiment of FIGS. 4A1 and 4A2, the pixelatedpolarization rotating array 9 is realized as an array ofelectronically-controlled circular polarization rotating elements 9″ forrotating the circularly polarized electric field along the LHCPdirection to the RHCP direction (or vice versa) as the light rays aretransmitted through the spatially corresponding pixels in the LCD panel.In the illustrative embodiment of FIGS. 4A1 and 4A2, eachelectronically-controlled circular polarization rotating element 9A″,9B″, 9C″ can be realized as a π-cell, whose operation is by controlledby a control voltage well known in the art. In its electrically-inactivestate (i.e. no-voltage is applied), the electric field intensity oflight exiting from the cell is substantially zero, thus a “dark”subpixel level is produced. In its electrically-active state (i.e. thethreshold voltage V_(T) is applied), the electric field intensity oflight exiting from the cell is substantially non-zero and thus a“bright” subpixel level is produced.

In the illustrative embodiment of FIG. 4A1 and 4A2, the array ofspectral filtering elements 10 is realized as a pixelated array ofpass-band circular polarizing reflective elements 10″ formed within asingle plane. Broad-band circularly polarizing reflective panel 11″ islaminated to the pixelated array of pass-band circular polarizingreflective elements 10″. As indicated in FIGS. 4A1 and A2, eachpass-band circular polarizing reflective element in the pixelatedpass-band circular polarizing panel 10″ has a LHCP characteristicpolarization state, whereas the broad-band circular polarizingreflective panel 8″ adjacent the backlighting structure has an LHCPcharacteristic polarization state, and broad-band circular polarizingreflective panel 10″ has a RHCP characteristic polarization state,indicated in FIGS. 4B and 4C.

As shown in FIG. 4D, each pass-band polarizing reflective element 10C″associated with a “blue” subpixel in the pixelated pass-band linearpolarizing panel 10C″ is particularly designed to reflect nearly 100%all spectral components having the LHCP characteristic polarizationstate and a wavelength within the green reflective band Δλ_(G) or thered reflective band Δλ_(R), whereas all spectral components having theLHCP characteristic polarization state or a wavelength within the bluereflective band Δλ_(B) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The manner in which the pass-bandpolarizing reflective element associated with each “blue” subpixel is“tuned” will be described hereinafter with reference to the method ofLCD panel fabrication illustrated in FIGS. 5, 6, 7A through 7C.

As shown in FIG. 4E, each pass-band polarizing reflective element 10B″associated with a “green” subpixel in the pixelated pass-band linearpolarizing panel 10″ is particularly designed to reflect nearly 100% allspectral components having the LHCP characteristic polarization stateand a wavelength within the red reflective band Δλ_(R) or the bluereflective band Δλ_(B), whereas all spectral components having the LHCPcharacteristic polarization state or a wavelength within the greenreflective band Δλ_(G) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The manner in which the pass-bandpolarizing reflective element associated with each “green” subpixel is“tuned” will be described hereinafter with reference to the method ofLCD panel fabrication illustrated in FIGS. 5, 6, 7A through 7C.

As shown in FIG. 4F, each pass-band polarizing reflective element 10A″associated with a “red” subpixel in the pixelated pass-band linearpolarizing panel 10″ is particularly designed to reflect nearly 100% allspectral components having the LHCP characteristic polarization stateand a wavelength within the green reflective band Δλ_(G) or the bluereflective band Δλ_(B), whereas all spectral components having the LHCPcharacteristic polarization state or a wavelength within the redreflective band Δλ_(R) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The manner in which the pass-bandpolarizing reflective element associated with each “red” subpixel is“tuned” will be described hereinafter with reference to the method ofLCD panel fabrication illustrated in FIGS. 5, 6, 7A through 7C.

SYSTEMIC LIGHT RECYCLING WITHIN THE LCD PANEL OF THE PRESENT INVENTION

The light transmission efficiency of prior art LCD panels has beenseverely degraded as a result of the following factors: absorption oflight energy due to absorption-type polarizers used in the LCD panels;absorption of light reflected off thin-film transistors (TFTs) andwiring of the pixelated spatial intensity modulation arrays used in theLCD panels; absorption of light by pigments used in the spectral filtersof the LCD panels; absorption of light energy by the black-matrix usedto spatially separate the subpixel filters in the LCD panel in order toenhance image contrast; and Fresnel losses due to the mismatching ofrefractive indices between layers within the LCD panels. As a result ofsuch light energy losses, it has been virtually impossible to improvethe light transmission efficiency of prior art LCD panels beyond about5%.

The LCD panel of the present invention overcomes each of the abovedrawbacks by employing a novel scheme of “systemic light recycling”which operates at all levels of the LCD system in order to avoid thelight energy losses associated with prior art LCD panel designs, andthereby fully utilize nearly 100% of the light energy produced by thebacklighting structure thereof. While the details of this novel systemiclight recycling scheme will be hereinafter described for each of theillustrative embodiments, it will be appropriate at this juncture tobriefly set forth the principles of this systemic light recyclingscheme.

In each of the embodiments of the present invention, a singlepolarization state of light is transmitted from the backlightingstructure to those structures (or subpanels) of the LCD panel wherespatial intensity modulation and spectral filtering function of thetransmitted polarized light simultaneously occurs on a subpixel basisand in a functionally integrated manner. At each subpixel location,spectral bands of light which are not transmitted to the display surfaceduring spectral filtering are reflected without absorption back alongthe projection axis into the backlighting structure where the polarizedlight is recycled with light energy being generated therewith and thenretransmitted from the backlighting structure into section of the LCDpanel where spatial intensity modulation and spectral filtering of theretransmitted polarized light simultaneously occurs on a subpixel basisin a functionally integrated manner. At each subcomponent level withinthe LCD panel, spectral components of transmitted polarized light whichare not used at any particular subpixel structure location areeffectively reflected either directly or indirectly back into thebacklighting structure for recycling with other spectral components forretransmission through the backlighting structure at the operativepolarization state, for reuse by both the same and neighboring subpixelstructures. The mechanics of this novel systemic light recycling schemeare schematically illustrated in FIGS. 3A1, 3A2, 4A1, 4A2, 9A1, 9A2, 11,12, 13 and 14, and will be described in greater detail hereinafter. Byvirtue of this novel systemic light recycling scheme of the presentinvention, it is now possible to design and construct LCD panels thatcan utilize produced backlight with nearly 100% light transmissionefficiency, in marked contrast with prior art LCD panels havingefficiencies of about 5%.

Apparatus For Fabricating The LCD Panels Hereof

FIG. 5 provides a schematic representation of a computer-controlledsystem 15 which can be used during the fabrication of the pixelatedpass-band (linear or circular) polarizing reflective panels 10′ and 10″hereof. As shown, the computer-controlled system 15 comprises a numberof subcomponents, namely: a fixture 16 for supporting a plate 17 thesize of the LCD panel to be fabricated, within the x-y plane of acoordinate reference frame embedded within the system; coating means 18(e.g. applicator technology) for coating one surface of the plate with aCLC mixture 19 containing in its liquid phase, liquid crystals,monomers, and other additives; a temperature-controlled oven 20 (with aUV transparent window), within which the CLC coated plate 17 can betransported and maintained for optical and thermal processing; asubpixel-exposure mask 21 having a pattern of apertures 21A, 21B and 21Cwhich spatially correspond with the red, green or blue subpixelstructures, respectively, of the LCD panel to be fabricated; asubpixel-array mask 21′ having a pattern of opaque subpixel regionswhich spatially correspond with the red, green or blue subpixelstructures formed on the CLC-coated plate of the LCD panel to befabricated; a mask translator 22 for precisely translating the masks 21and 21′ relative to the fixture along the x and y axes of the system; asource of ultraviolet (UV) radiation 23 for producing a focused beam ofUV radiation having a specified bandwidth, for exposing the layer of CLCmaterial 19 upon the plate supported within the fixture, while the CLClayer is precisely maintained at a preselected temperature; atemperature controller 24 for controlling the temperature of theinterior of the oven 20 and thus the layer of CLC material coated on theplate; and a system controller 25 for controlling the operation of themask translator 22 and temperature controller 24 during the fabricationprocess.

The primary function of this system 15 is to control the temperature ofthe CLC coated plate 17 and its UV exposure at each of the threesubpixel filter fabrication stages involved in the fabrication of panel10. In particular, during the “red” subpixel processing stage, the mask21 is translated relative to the CLC coated plate 17 so allow producedUV radiation to expose only the red subpixel regions on the CLC coatedplate, while the CLC coating is maintained at temperature T_(R),determined from the characteristic shown in FIG. 6. During the “green”subpixel processing stage, the mask 21 is translated relative to the CLCcoated plate 17 so allow produced UV radiation to expose only the greensubpixel regions on the CLC coated plate 17, while the CLC coating ismaintained at temperature T_(G), determined from the characteristicshown in FIG. 6. During the “blue” subpixel processing stage, the maskis translated relative to the CLC coated plate so allow produced UVradiation to expose only the red subpixel regions on the CLC coatedplate, while the CLC coating is maintained at temperature T_(R),determined from the characteristic shown in FIG. 6. During the “pixelmatrix” processing stage, mask 21 is removed and mask 21′ positionedrelative to the CLC-coated plate so allow produced UV radiation toexpose at the required UV-light intensity I_(BB), only the subpixelintersticial regions on the CLC coated plate, while the CLC coating ismaintained at temperature T_(BB), determined from the characteristicsand properties of the CLC mixture used.

For each RHLP or LHCP CLC mixture to be used to make the pixelatedpass-band circularly polarizing reflective panel 10, the graphical plotof FIG. 6 is empirally acquired by analytical procedures well known inthe CLC art. Having acquired this wavelength versus UV-exposuretemperature plot for any given CLC mixture, the LCD panel designer caneasily determine: (1) the UV-exposure temperature required in order totune the subpixel filters to transmit only over the narrow “red”spectral pass-band Δλ_(R), while reflecting all other wavelengthswithout energy loss or absorption; (2) the UV-exposure temperaturerequired in order to tune the subpixel filters to transmit only over thenarrow “green” spectral pass-band Δλ_(G), while reflecting all otherwavelengths without energy loss or absorption; and (3) the UV-exposuretemperature required in order to tune the subpixel filters to transmitonly over the narrow “blue” spectral pass-band Δλ_(B), while reflectingall other wavelengths without energy loss or absorption.

Method Of Fabricating The LCD Panels Hereof

Referring now to FIGS. 7A through 7C, a preferred fabrication methodwill now be described for the LCD panel illustrated in FIGS. 2, 3A1 and3A2.

As indicated at Block A of FIG. 7A, the first step of the fabricationmethod involves applying a layer of the selected CLC-mixture onto thesurface of an optically-transparent support substrate (e.g. glass plate)having length and width dimensions equal to the size of the LCD panel tobe fabricated. Methods for selecting and mixing the CLC components ofthe CLC mixture are described in: U.S. Letters Patent No. 5,691,789,supra; the SID publication entitled “Cholesteric Reflectors with a ColorPattern” by R. Maurer, F-H Kreuzer and J. Stohrer published at pages399-402 of SID 94 DIGEST (1994); and the SID publication entitled“Polarizing Color Filters Made From Cholesteric LC Silicones” by RobertMaurer, Dirk Andrejewski, Franz-Heinrich Kreuzer, and Alfred Miller, atpages 110-113 of SID 90 DIGEST (1990).

At Block B in FIG. 7A, the CLC-coated plate 17 is loaded into the ovenshown in FIG. 5 which is operated to maintain its temperature at T_(B)indicated in FIG. 6. As indicated in Block C, the mask 21 is translatedinto position over the CLC-coated plate 17 for exposure to UV radiationto form an array of pass-band polarizing reflective elements tuned tothe blue spectral-band Δλ_(B). Then at Block D, the CLC-coated plate 17is exposed to UV light through the mask positioned for forming pass-bandpolarizing reflective elements tuned to the blue spectral-band Δλ_(B).

At Block E, the mask 21 is translated into position over the CLC-coatedplate 17 for exposure to UV radiation to form an array of pass-bandpolarizing reflective elements tuned to the green spectral-band Δλ_(G).Then at Block F, the oven temperature T_(G) is selected and the CLCcoated plate is allowed to reach this temperature. At Block, theCLC-coated plate 17 is exposed to UV light through the mask positionedfor forming pass-band polarizing reflective elements tuned to the greenspectral-band Δλ_(G).

At Block H, the mask 21 is translated into position over the CLC-coatedplate 17 for exposure to UV radiation to form an array of pass-bandpolarizing reflective elements tuned to the red spectral-band Δλ_(R).Then at Block I, the oven temperature is T_(R) is selected and the CLCcoated plate is allowed to reach this temperature. At Block in FIG. 7A,the CLC-coated plate is exposed to UV light through the mask positionedfor forming pass-band polarizing reflective elements tuned to the redspectral-band Δλ_(R).

At Block K in FIG. 7B, the subpixel-exposure mask 21 is removed and thepixel-array mask 21′ installed above the CLC-coated plate. Then at BlockL, the oven temperature is adjusted to T_(BB) and the CLC-coated plateallowed to attain this temperature. Temperature T_(BB) can be determinedin accordance with the teaching disclosed in Applicant's U.S. LettersPatent No. 5,691,789, supra, so that a broad-band polarizing reflectioncharacteristics will be imparted to the CLC-coating over thoseunprotected regions determined by mask 21′. At Block M, the intensity ofthe UV light is set to the value I_(BB) required to achieve broad-bandoperation using the particular CLC-mixture at exposure temperatureT_(BB) . Similarly, light intensity I_(BB) can be determined inaccordance with the teaching disclosed in Applicant's U.S. LettersPatent No. 5,691,789, supra. Then at Block N the CLC-coated plate isexposed to the UV light at intensity I_(BB) and temperature T_(BB) toform a broad-band polaring reflective region between the interstices ofthe subpixel filter elements formed on the CLC-coated plate. Notably,this reflective region will be designed to reflect the polarized lighttransmitted from the backlighting structure so that it can be recycledand reused in accordance with the principles of the present invention.

At Block O, the exposed CLC-coated plate is removed from the oven andallowed to cool to room temperature. At this stage, a CLC panel isprovided having formed therein, three spatially arranged arrays ofpass-band circularly-polarizing reflective elements (i.e. subpixelspectral filter elements) along a single plane with a polarizingreflective matrix-mask region formed therebetween for improving imagecontrast while systemically recycling polarized light which does notcontribute to the formation of image structure. Each array of pass-bandcircularly-polarizing reflective elements is adapted for use in the LCDpanel embodiments of FIGS. 4A1 and 4A2. The first array is tuned toreflect only RH (or LH) circularly polarized spectral components havinga wavelength in the red spectral-band Δλ_(R); the second array is tunedto reflect only RH (or LH) circularly polarized spectral componentshaving a wavelength in the green spectral-band Δλ_(G); and the thirdarray is tuned to reflect only RH (or LH) circularly polarized spectralcomponents having a wavelength in the blue spectral-band Δλ_(B). Asindicated at Block P in FIG. 7B, in order that each one of thesesubpixel filter elements reflects linearly polarized light as requiredin the LCD panel embodiments of FIGS. 3A1 and 3A2, 9A1 and 9A2, 11 and13, rather than circularly polarized light, it is necessary to impart aπ/2 (i.e. quarter-wave) phase retardation region (or structure) to eachone of these elements in order to impart a linear polarization statethereto. Such circular-to-linear polarization conversion can be achievedby laminating onto the spatially-arranged arrays of pass-bandcircularly-polarizing reflective elements (i.e. subpixel filterelements), a first quarter-wave phase retardation panel patternedaccording to the composite subpixel pattern of the spectral filteringarray. This will fabrication step will effectively convert the circularpolarization state of each spectral filter element in the polarizingreflective spectral filtering array to the appropriate linearpolarization state called for by the LCD panel design underconstruction. Similarly, a second quarter-wave phase retardation panel,patterned according to the subpixel interstice pattern, can beappropriately laminated onto the first quarter-wave pattern, in order toconvert the circular polarization state of the circularly polarizingreflective subpixel interstice pattern to the appropriate linearpolarization state called for by the LCD panel design underconstruction. An excellent tutorial and overview on thepolarization-reflective properties of CLC materials and principles ofpolarization state conversion (i.e. linear-to-circular,circular-to-linear, linear-to-linear, circular-to-circular,unpolarized-to-linear, and unpolarized-to-circular) can be found inApplicant's U.S. Pat. No. 5,221,982, incorporated herein by reference.At the end of this stage of the fabrication method, the result is anarray of linearly-polarized reflective elements tuned to the particularspectral band.

In the event that LCD panels of the type shown in FIGS. 3A1 and 3A2, 9A1and 9A2, 11 and 13 are being constructed (rather than the LCD panels ofFIGS. 4A1 and 4A2, 10A1 and 10A2, 12 and 14), it will be necessary touse linear, rather than circular, polarization principles therein. Insuch cases, it will be necessary to realize a pixelated array of “linearpolarization” rotating elements, rather than a pixelated array ofcircular polarization rotating elements (i.e. an array of π-cells) as asubcomponent of the LCD panel system. For purposes of illustration,however, the balance of the description of the fabrication method hereofwill be directed to the fabrication of the LCD panel of FIGS. 3A1 and3A2. It will be understood, however, that to fabricate an LCD panelusing circular polarization rotating elements (i.e. an array ofπ-cells), the illustrative fabrication method will be modified in wayswhich involve the fabrication of an array of circular polarizationrotating elements in a manner well known in the art.

At Block Q in FIG. 7B, an ITO layer is applied to the surface of theCLC-coated panel 17 produced at Block X. Then at Block R of FIG. 7C, apolyamide alignment layer is applied to the ITO layer. At Block S inFIG. 7C, a patterned layer of ITO is applied to the surface of a secondglass plate the same size as the glass plate supporting the CLC-layer.The pattern of ITO material corresponds to the composite subpixelpattern of the pixelated spectral filter array fabricated above. Then atBlock T, a layer of liquid crystal (LC) material of a prespecifiedthickness is applied to the previously applied polyamide layer.

At Block U of FIG. 7C, the ITO layer on the second glass plate isbrought into physical contact with the LC layer in order to construct atwisted nematic (TN) or super-twisted nematic (STN) array with aspectral filtering array formed thereon. Then at Block V, electricallyconductive electrodes are attached to the patterned ITO layer in aconventional manner to provide.

At Block in FIG. 7C, the first broad-band linear polarizing reflectorpanel 8″ (prefabricated) is attached to the second surface of the secondoptically transparent plate. At Block , the second broad-band linearpolarizing reflector panel 11 (prefabricated) is attached to the secondsurface of the first optically transparent plate on which the spectralfiltering array has been previously formed during the fabricationmethod. Then at Block Y, the first broad-band linear polarizingreflector panel (prefabricated) 8′ is mounted to the backlightingstructure being used. In the illustrative embodiments, this stepinvolves mounting the first broad-band linear polarizing reflector panelto the light guiding panel 7B of the backlighting structure 7, providinga slight air gap between the interfaced optical surfaces. Thequasi-diffusive reflector 7A associated with the backlighting structurecan be directly mounted on the rear surface of the light guiding panel,as illustrated in FIGS. 2 and 3A1 and 3A2.

Upon completing the steps of the above-described fabrication process,the LCD panel shown in FIGS. 3A1 and 3A2 is provided. Manufacture of theLCD panel shown in FIGS. 4A1 and 4A2 can be carried out much in the sameway as described above with one minor exception. As circularlypolarizing reflective panels are used in this particular embodiment,there is no need to impart a quarter-wave phase retardation to thepass-band circularly polarizing reflective elements 9A, 9B 9C. Also, thebroad-band circularly polarizing reflective panels 8″ and 11″, ratherthan panels 8′ and 11′, are used to construct the LCD panel of thepresent invention.

While the above described method has described forming the pixelatedarray of pass-band polarizing reflecting elements within a single layerof CLC material, it may be desirable in particular applications to makethis pixelated reflective filtering array by using alternativefabrication techniques including photolithography, screen-printing,gravure printing and other methods known in the art. When using suchalternative techniques, a pixelated polarizing reflective array ofsubpixel filter elements can be separately fabricated for each spectralband (e.g. red, green and blue) to provide three panels each embodying asubpixel filtering array tuned to a particular band along the opticalspectrum. These subpixel spectral filter arrays can then be aligned inproper registration and bonded together through laminatation techniquesto form a composite structure having pass-band polarizing-reflectiveproperties similar to those exhibited by the pixelated passed-bandreflecting filter array of unitary construction described above.

Operation Of The First And Second Illustrative Embodiments of the LCDPanel of the First Generalized Embodiment of the Present Invention

Having described in detail how to make the LCD panels illustrated inFIGS. 2, 3A1, 3A2, and 4A1 and 4A2, it is appropriate at this junctureto now describe their operation with reference to the exemplary pixelstructure detailed in such figure drawings.

As shown in FIGS. 3A1 and 3A2, unpolarized light is produced within thebacklighting structure and is composed of spectral components havingboth LP1 and LP2 polarization states. Only spectral components havingthe LP2 polarization state are transmitted through the broad-band linearpolarizing reflective panel 8′ adjacent the backlighting panel 7,whereas spectral components having polarization state LP1 incidentthereon are reflected therefrom without energy loss or absorption.Spectral components reflecting off broad-band linear polarizingreflective panel 8′ on the backlighting structure side strikequasi-diffusive reflector 7A, and undergo a polarization inversion (LP1to LP2). This reflection process occurs independent of wavelength. Thespectral components which were inverted from LP1 to LP2 having the LP2polarization state are transmitted through the broad-band linearpolarizing reflective panel 8′ adjacent the backlighting structure.

When a linear polarization rotating element 10A, 10B and 10C associatedwith a red, green or blue subpixel is driven into its inactive-state asshown in FIG. 3A1, the polarization rotating element associatedtherewith transmits the spectral components therethrough independent ofwavelength while effecting an orthogonal conversion in polarizationstate (i.e. LP1 to LP2 and LP2 to LP1) and producing a “dark” subpixellevel in response to the inactive-state into which it has been driven.

When a “red” subpixel is driven into its “dark” state shown in FIG. 3A1,spectral components within the backlighting panel having wavelengthswithin the “red”, “green” or “blue” band Δλ_(R) and polarization stateLP2 (i.e. λ_(R) ^(LP2)) are transmitted through the broad-band linearlypolarizing reflective panel 8′, the “red” pass-band linearly polarizingreflective element 10A′ and reflect off broad-band linearly polarizingreflective panel 11′ without absorption. The reflected “red”, “green”and “blue” spectral components with the LP2 polarization state (i.e.λ_(R) ^(LP2), λ_(G) ^(LP2), λ_(B) ^(LP2)) are retransmitted throughpass-band linearly polarizing reflective element 10A′, linearpolarization rotating element 9A′, and broad-band linearly polarizingreflective panel 8′ back into the backlighting structure for systemicrecycling.

When a “green” subpixel is driven into its “dark” state shown in FIG.3A1, spectral components within the backlighting panel havingwavelengths within the “red”, “green” or “blue” band Δλ_(R) andpolarization state LP2 (i.e. λ_(R) ^(LP2)) are transmitted through thebroad-band linearly polarizing reflective panel 8′ and the “green”pass-band linearly polarizing reflective element 10B′ and then reflectoff broad-band linearly polarizing reflective panel 11′ withoutabsorption. These reflected “red”, “green” and “blue” spectralcomponents with the LP2 polarization state (i.e. λ_(R) ^(LP2), λ_(G)^(LP2), λ_(B) ^(LP2)) are retransmitted through pass-band linearlypolarizing reflective element 10B′, linear polarization rotating element9B′, and broad-band linearly polarizing reflective panel 8′ back intothe backlighting structure for systemic recycling.

When a “blue” subpixel is driven into a “dark” state shown in FIG. 3A1,spectral components within the backlighting panel having wavelengthswithin the “red”, “green” or “blue” band Δλ_(R) and polarization stateLP2 (i.e. λ_(R) ^(LP2)) are transmitted through the broad-band linearlypolarizing reflective panel 8′ and the “blue” pass-band linearlypolarizing reflective element 10C′ and then reflect off broad-bandlinearly polarizing reflective panel 11′ without absorption. Thesereflected “red”, “green” and “blue” spectral components with the LP2polarization state (i.e. λ_(R) ^(LP2), λ_(G) ^(LP2), λ_(B) ^(LP2)), areretransmitted through pass-band linearly polarizing reflective element10C′, linear polarization rotating element 9C′, and broad-band linearlypolarizing reflective panel 8′ back into the backlighting structure forsystemic recycling.

When a linear polarization rotating element is controlled in itsactive-state as shown in FIG. 3A2, the element transmits the spectralcomponents therethrough independent of wavelength without effecting aconversion in polarization state, producing a “bright” subpixel level inresponse to the active-state into which it has been driven.

When a “red” subpixel is driven into its “bright” state as shown in FIG.3A2, spectral components within the backlighting panel havingwavelengths within the “red” band Δλ_(R) and a polarization state LP2(i.e. λ_(R) ^(LP2)) are transmitted through the broad-band linearlypolarizing reflective panel 8′, the linear polarization rotating element9A′, the “red” pass-band linearly polarizing reflective element 10A′ andthe broad-band linearly polarizing reflective panel 11′ withoutabsorption. In this state, spectral components within the backlightingstructure having wavelengths within the “green” band Δλ_(G) or “blue”band Δλ_(B) and a polarization state LP2 (i.e. λ_(G) ^(LP2), λ_(B)^(LP2)) are transmitted through the broad-band linear polarizingreflective panel 8′, the linear polarization rotating element 9A′ andreflected off the “red” pass-band linearly polarizing reflective element10A′ and retransmitted through the linear polarization rotating element9A′ and broad-band linear polarizing reflective panel 8′ back into thebacklighting structure for systemic recycling.

When a “green” subpixel is driven into its “bright” state as shown inFIG. 3A2, spectral components within the backlighting structure havingwavelengths within the “green” band Δλ_(G) and a polarization state LP2(i.e. λ_(G) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the linear polarization rotating element9B′, the “green” pass-band linearly polarizing reflective element 10B′and the broad-band linearly polarizing reflective panel 11′ withoutabsorption. In this state, spectral components within the backlightingstructure having wavelengths within the “red” band Δλ_(R) or “blue” bandΔλ_(B) and a polarization state LP2 (i.e. λ_(R) ^(LP2) λ_(B) ^(LP2)) aretransmitted through the broad-band linear polarizing reflective panel 8′and the linear polarization rotating element 9B′ and reflected off the“green” pass-band linearly polarizing reflective element 10B′ andretransmitted through the linear polarization rotating element 9B′ andbroad-band linear polarizing reflective panel 8′ back into thebacklighting structure for systemic recycling.

When a “blue” subpixel is driven into its “bright” state as shown inFIG. 3A2, spectral components within the backlighting structure havingwavelengths within the “blue” band Δλ_(B) and a polarization state LP2(i.e. λ_(B) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the linear polarization rotating element9C′, the “blue” pass-band linearly polarizing reflective element 10C′and the broad-band linearly polarizing reflective panel 11′ withoutabsorption. In this state, spectral components within the backlightingstructure having wavelengths within the “red” band Δλ_(R) or “green”band Δλ_(G) and a polarization state LP2 (i.e. λ_(R) ^(LP2) λ_(G)^(LP2)) are transmitted through the broad-band linear polarizingreflective panel 8′ and the linear polarization rotating element 9C′ andreflected off the “blue” pass-band linearly polarizing reflectiveelement 10C′ and retransmitted through the linear polarization rotatingelement 9C′ and broad-band linearly polarizing reflective panel 8′ backinto the backlighting structure for systemic recycling.

As shown in FIGS. 4A1 and 4A2, unpolarized light is produced within thebacklighting structure and is composed of spectral components havingboth LHCP and RHCP polarization states. Only spectral components havingthe RHCP polarization state are transmitted through the broad-bandcircularly polarizing reflective panel 8″ adjacent the backlightingpanel 7, whereas spectral components having polarization state RHCPincident thereon are reflected therefrom without energy loss orabsorption. Spectral components reflecting off broad-band circularlypolarizing reflective panel 8″ on the backlighting structure side strikequasi-diffusive reflector 7A, and undergo a polarization inversion (i.e.LHCP to RHCP or RHCP to LHCP). This reflection process occursindependent of wavelength. The spectral components having the RHCPpolarization state are transmitted through the broad-band circularlypolarizing reflective panel 8″.

When a circular polarization rotating element associated with a red,green or blue subpixel is driven into its inactive-state as shown inFIG. 4A1, the polarization rotating element associated therewithtransmits the spectral components therethrough independent of wavelengthwhile effecting an orthogonal conversion in polarization state (i.e.LHCP to RHCP and RHCP to LHCP), thereby producing a “dark” subpixellevel in response to the inactive-state into which it has been driven.

When a “red” subpixel is driven into its “dark” state shown in FIG. 4A1,spectral components within the backlighting structure having wavelengthswithin the “red”, “green” or “blue” band Δλ_(R) and polarization stateRHCP (i.e. λ_(R) ^(RHCP)) are transmitted through the broad-bandcircular polarizing reflective panel 8″, the circular polarizationrotating element 9A″ and the “red” pass-band circularly polarizingreflective element 10A″ and reflect off broad-band circularly polarizingreflective panel 11″ without absorption. These reflected “red”, “green”and “blue” spectral components with the RHCP polarization state (i.e.λ_(R) ^(RHCP), λ_(G) ^(RHCP), λ_(B) ^(RHCP)) are retransmitted throughpass-band circularly polarizing reflective element 10A″, circularpolarization rotating element 9A″, and broad-band circularly polarizingreflective panel 8″ back into the backlighting structure for systemicrecycling.

When a “green” subpixel is driven into its “dark” state shown in FIG.4A1, spectral components within the backlighting structure havingwavelengths within the “red”, “green” or “blue” band and polarizationstate RHCP (i.e. λ_(R) ^(RHCP), λ_(G) ^(RHCP), λ_(B) ^(RHCP)) aretransmitted through the broad-band circular polarizing reflective panel8″, circular polarization rotating element 9B″ and the “green” pass-bandcircularly polarizing reflective element 10B″ and reflect off broad-bandcircularly polarizing reflective panel 11″ without absorption. Thesereflected “red”, “green” and “blue” spectral components with the LHCPpolarization state (i.e. λ_(R) ^(RHCP), λ_(G) ^(RHCP), λ_(B) ^(RHCP))are retransmitted through pass-band circularly polarizing reflectiveelement 10B″, circular polarization rotating element 9B″, and broad-bandcircularly polarizing reflective panel 8″ back into the backlightingstructure for systemic recycling.

When a “blue” subpixel is driven into a “dark” state shown in FIG. 4A1,spectral components within the backlighting structure having wavelengthswithin the “red”, “green” or “blue” band Δλ_(R) and polarization stateRHCP (i.e. λ_(R) ^(RHCP), λ_(G) ^(RHCP), λ_(B) ^(RHCP)) are transmittedthrough the broad-band circular polarizing reflective panel 8″, circularpolarization rotating element 9C″, the “blue” pass-band circularlypolarizing reflective element 10C″ and reflect off broad-band circularlypolarizing reflective panel 11″ without absorption. These reflected“red”, “green” and “blue” spectral components with the RHCP polarizationstate (i.e. λ_(R) ^(RHCP), λ_(G) ^(RHCP), λ_(B) ^(RHCP)P) areretransmitted through pass-band circularly polarizing reflective element10C″, circular polarization rotating element 9C″, and broad-bandcircularly polarizing reflective panel 8″ back into the backlightingstructure for systemic recycling.

When a circular polarization rotating element is controlled in itsactive-state as shown in FIG. 4A2, the element transmits the spectralcomponents therethrough independent of wavelength without effecting aconversion in polarization state, thereby producing a bright subpixellevel in response to the active-state into which it has been driven.

When a “red” subpixel is driven into its “bright” state as shown in FIG.4A2, spectral components within the backlighting structure havingwavelengths within the “red” band Δλ_(R) and a polarization state RHCP(i.e. λ_(R) ^(RHCP)) are transmitted through the broad-band circularpolarizing reflective panel 8″, circular polarization rotating element9A″, the “red” pass-band circularly polarizing reflective element 10A″and the broad-band circularly polarizing reflective panel 11′ withoutabsorption. In this state, spectral components within the backlightingstructure having wavelengths within the “green” band Δλ_(G)) or “blue”band Δλ_(B) and a polarization state RHCP (i.e. λ_(G) ^(RHCP) λ_(B)^(RHCP)) are transmitted through the broad-band circular polarizingreflective panel 8″ and the circular polarization rotating element 9A″and reflected off the “red” pass-band circularly polarizing reflectiveelement 10A″ and retransmitted through the circular polarizationrotating element 9A″ and broad-band circularly polarizing reflectivepanel 8″ back into the backlighting structure for systemic recycling.

When a “green” subpixel is driven into its “bright” state as shown inFIG. 4A2, spectral components within the backlighting structure havingwavelengths within the “green” band Δλ_(G) and a polarization state RHCP(i.e. λ_(G) ^(RHCP)) are transmitted through the broad-band circularpolarizing reflective panel 8″, the circular polarization rotatingelement 9B″, the “green” pass-band circularly polarizing reflectiveelement 10B″ and the broad-band circularly polarizing reflective panel11″ without absorption. In this state, spectral components within thebacklighting structure having wavelengths within the “red” band Δλ_(R)or “blue” band Δλ_(B) and a polarization state RHCP (i.e. λ_(R) ^(RHCP)λ_(B) ^(RHCP)) are transmitted through the broad-band circularpolarizing reflective panel 8″ and the circular polarization rotatingelement 9B″ and reflected off the “green” pass-band circularlypolarizing reflective element 10B″ and retransmitted through thecircular polarization rotating element 9B″ and broad-band circularlypolarizing reflective panel 8″ back into the backlighting structure forsystemic recycling.

When a “blue” subpixel is driven into its “bright” state as shown inFIG. 4A2, spectral components within the backlighting structure havingwavelengths within the “blue” band Δλ_(B) and a polarization state RHCP(i.e. λ_(B) ^(RHCP)) are transmitted through the broad-band circularpolarizing reflective panel 8″, the circular polarizing rotating element10C″, the “blue” pass-band circularly polarizing reflective element 9C″and the broad-band circularly polarizing reflective panel 11″ withoutabsorption. In this state, spectral components within the backlightingstructure having wavelengths within the “red” band Δλ_(R) or “green”band Δλ_(G) and a polarization state RHCP (i.e. λ_(R) ^(RHCP) λ_(G)^(RHCP)) are transmitted through the broad-band circular polarizingreflective panel 8″ and the circular polarization rotating element 9C″and reflected off the “blue” pass-band circularly polarizing reflectiveelement 10C″ and retransmitted through the circular polarizationrotating element 9C″ and broad-band circularly polarizing reflectivepanel 8″ back into the backlighting structure for systemic recycling.

Overview on the LCD Panel Construction of FIG. 8

In the second generalized LCD panel construction shown in FIG. 8,spectral filtering occurs before spatial intensity modulation. In thesecond illustrative embodiment of this LCD panel construction shown inFIGS. 9A1 and 9A2, linear polarization techniques are used to carry outthe spatial intensity modulation and spectral filtering functionsemployed therein. In the second illustrative embodiment of this LCDpanel construction shown in FIGS. 10A1 and 10A2, circular polarizationtechniques are used to carry out the spatial intensity modulation andspectral filtering functions employed therein. In each such illustrativeembodiment, modifications are made among the various components of theLCD panel shown in FIG. 8. Details regarding such modifications will bedescribed hereinafter.

In FIG. 8, the subcomponent structure of the second generalizedembodiment of the LCD panel hereof is shown in great clarity. As shown,the second generalized embodiment of the LCD panel 2 comprises: abacklighting structure 7 including a quasi-diffusive reflector 7A, forproducing a plane of broad-band light having a substantially uniformlight intensity over the x and y coordinate axes thereof; a broad-bandpolarizing reflective panel 8; a pixelated array 10 of pass-bandpolarizing reflective (filter) elements 10A, 10B, 10C, for spectralfiltering of light produced from the backlighting structure; a pixelatedarray 9 of polarization direction rotating elements 9A, 9B, 9C forspatial intensity modulation of light produced from the pixelated arrayof pass-band polarizing reflective (filter) elements; and a broad-bandpolarizing reflective panel 11 for cooperative operation with thepixelated array of polarization direction rotating elements 9 and thepixelated array of pass-band polarizing reflective (filter) elements 10.

In order to produce high-resolution color images, the spatial period ofthe pixelated arrays 9 and 10 is selected to be relatively small inrelation to the overall length and height dimensions of the LCD panel.In a conventional manner, each pixel structure in the LCD panel iscomprised of a red subpixel 13A, a green subpixel 13B and blue subpixel13C, as illustrated in FIG. 2A. As shown therein, each red subpixelstructure 13A comprises a red-band spectral filtering element 10A whichis spatially registered with a first polarization direction rotatingelement 9A. Each green subpixel structure 13B comprises a green-bandspectral filtering element 10B spatially registered with a secondpolarization direction rotating element 9B. Each blue subpixel element13C comprises a blue-band spectral filtering element 10C spatiallyregistered with a third polarization direction rotating element 9C. Theoutput intensity (i.e. brightness or darkness level) of each redsubpixel structure is controlled by applying pulse-width modulatedvoltage signal V_(R) to the electrodes of its electrically-controlledspatially intensity modulating element. The output intensity of eachgreen subpixel structure is controlled by applying pulse-width modulatedvoltage signal V_(G) to the electrodes of its electrically-controlledspatially intensity modulating element. The output intensity of eachblue subpixel structure is controlled by providing pulse-width modulatedvoltage signal V_(B) applied to the electrodes of itselectrically-controlled spatially intensity modulating element. Bysimply controlling the width of the above-described voltages V_(R),V_(G), V_(B), the grey-scale intensity (i.e. brightness) level of eachsubpixel structure can be controlled in a manner well known in the LCDpanel art.

First Illustrative Embodiment Of the LCD Panel Construction of FIG. 8

In the illustrative embodiments shown in FIGS. 9A1 and 9A2, thebacklighting structure 7 is realized in a manner described above.Understandably, there are other techniques for producing a plane ofunpolarized light for use in connection with the LCD panel of thepresent invention.

In the illustrative embodiment of FIG. 9A1 and 9A2, the pixelated arrayof polarization rotating elements 9 is realized as an array of linearpolarization rotating elements 9′ formed within a single plane. Asindicated in FIGS. 9A1 and 9A2, each pass-band linear polarizingreflective element 9A′, 9B′, 9C′ in the pixelated pass-band linearpolarizing panel 9′ has a LP2 characteristic polarization state, whereasthe broad-band linear polarizing reflective panel 8′ adjacent thebacklighting structure has an LP1 characteristic polarization state andthe broad-band linear polarizing reflective panel 11′ has an LP2characteristic polarization state.

A preferred method of making the broad-band linearly polarizingreflective panels 8′ and 11′ is disclosed in great detail in U.S.Letters Patent No. 5,691,789, entitled “Single Layer Reflective SuperBroadband Circular Polarizer and Method of Fabrication Therefor” bySadeg M. Faris and Le Li filed Oct. 30, 1995, which is incorporatedherein by reference in its entirety. An alternative method of makingbroad-band linearly polarizing reflective panels 8′ and 11′ is disclosedin EPO Application No. 94200026.6 entitled “Cholesteric Polarizer andManufacture Thereof”. The reflection characteristics of the broad-bandlinearly polarizing reflective panel 8′ are graphically illustrated inFIG. 9B for incident light having linear polarization state LP1, whereasthe reflection characteristics of the broad-band linearly polarizingreflective panel 11′ are graphically illustrated in FIG. 9C for incidentlight having linear polarization state LP2.

In the illustrative embodiment of FIGS. 9A1 and 9A2, the polarizationrotating array 9 is realized as an array of electronically-controlledlinear polarization rotating elements 9A′, 9B′, 9C′ for rotating thelinearly polarized electric field along LP1 to the LP2 polarizationdirection as the light rays are transmitted through the spatiallycorresponding pixels in the LCD panel. In the illustrative embodiment ofFIGS. 9A1 and 9A2, each electronically-controlled linear polarizationrotating element can be realized as a twisted nematic (TN) liquidcrystal cell, super-twisted nematic (STN) liquid crystal cell, orferro-electric cell, whose operation is by controlled by a controlvoltage well known in the art. To construct the linear polarizationrotating elements, thin film transistors (TFTs) can be used to createthe necessary voltages across a layer of liquid crystal material toachieve alignment of the liquid crystal molecules and thus cause thecorresponding element to not rotate the polarization direction oftransmitted light passing therethrough. In its electrically-inactivestate (i.e. no voltage is applied), the electric field intensity oflight exiting from the cell is substantially zero and thus a “dark”subpixel level is produced. In its electrically-active state (i.e. thethreshold voltage V_(T) is applied), the electric field intensity oflight exiting from the cell is substantially non-zero and thus a“bright” subpixel level is produced.

In the illustrative embodiment of FIG. 9A1 and 9A2, the pixelated arrayof spectral filtering elements 10 is realized as an array of pass-bandlinear polarizing reflective elements 10A′, 10B′, 10C′ formed within asingle plane. Broad-band linearly polarizing reflective panel 11′ islaminated to the pixelated array of spectral filtering elements 10.

As shown in FIG. 9D, each pass-band polarizing reflective element 10C′associated with a “blue” subpixel in the pixelated pass-band linearpolarizing panel 10′ is particularly designed to reflect nearly 100% allspectral components having the LP2 characteristic polarization state anda wavelength within the green reflective band Δλ_(G) or the redreflective band Δλ_(R), whereas all spectral components having the LP2characteristic polarization state and a wavelength within the bluereflective band Δλ_(B) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The pass-band polarizing reflectiveelement associated with each “blue” subpixel is “tuned” duringfabrication in the manner described hereinabove.

As shown in FIG. 9E, each pass-band polarizing reflective element 10B′associated with a “green” subpixel in the pixelated pass-band linearpolarizing panel 10″ is particularly designed to reflect nearly 100% allspectral components having the LP2 characteristic polarization state anda wavelength within the red reflective band Δλ_(R) or the bluereflective band Δλ_(B), whereas all spectral components having the LP2characteristic polarization state and a wavelength within the greenreflective band Δλ_(G) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The pass-band polarizing reflectiveelement associated with each “green” subpixel is “tuned” duringfabrication in the manner described hereinabove.

As shown in FIG. 9F, each pass-band polarizing reflective element 10C′associated with a “red” subpixel in the pixelated pass-band linearpolarizing panel 10′ is particularly designed to reflect nearly 100% allspectral components having the LP2 characteristic polarization state anda wavelength within the green reflective band Δλ_(G) or the bluereflective band, whereas all spectral components having the LP2characteristic polarization state and a wavelength within the redreflective band Δλ_(R) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The pass-band polarizing reflectiveelement associated with each “red” subpixel is “tuned” duringfabrication in the manner described hereinabove.

The pixelated pass-band linear polarizing reflective panel 9′ can befabricated in a manner similar to the way described in the LCD panelfabrication method described hereinabove.

Second Illustrative Embodiment Of the LCD Panel Construction of FIG. 8

In the illustrative embodiments shown in FIGS. 10A1 and 10A2, thebacklighting structure 7 is realized in a manner described above.Understandably, there are other techniques for producing a plane ofunpolarized light for use in connection with the LCD panel of thepresent invention.

In the illustrative embodiment of FIGS. 10A and 10A2, the pixelatedpolarization rotating array 9 shown in FIG. 8 is realized as an array ofelectronically-controlled circular polarization rotating elements 9″which rotate the circularly polarized electric field from the LHCPdirection to the RHCP direction as the light rays are transmittedthrough the spatially corresponding pixels in the LCD panel. In theillustrative embodiment of FIGS. 10A1 and 10A2, eachelectronically-controlled circular polarization rotating element 9A″,9B″, 9C″ can be realized as a π-cell, whose operation is by controlledby a control voltage well known in the art. In its electrically-inactivestate (i.e. no-voltage is applied), the electric field intensity oflight exiting from each π cell is substantially zero and thus a “dark”level is produced. In its electrically-active state (i.e. thresholdvoltage V_(T) is applied), the electric field intensity of light exitingfrom the cell is substantially non-zero and thus a “bright” subpixellevel is produced.

In the illustrative embodiment of FIG. 10A1 and 10A2, the array ofspectral filtering elements 10A″, 10B″, 10C″ is realized as an array ofpass-band circularly polarizing reflective elements 10″ formed within asingle plane. As indicated in FIGS. 10A1 and 10A2, each pass-bandcircularly polarizing reflective element in the pixelated pass-bandcircularly polarizing panel 10″ has a RHCP characteristic polarizationstate, whereas the broad-band circularly polarizing reflective panel 8″adjacent backlighting panel 7 has an LHCP characteristic polarizationstate and the broad-band circularly polarizing reflective panel 11″ hasa characteristic polarization state RHCP.

As shown in FIG. 10D, each pass-band polarizing reflective element 10C″associated with a “blue” subpixel in the pixelated pass-band circularlypolarizing panel 10 is particularly designed to reflect nearly 100% allspectral components having the RHCP characteristic polarization stateand wavelengths within the green reflective band Δλ_(G) and the redreflective band Δλ_(R), whereas all spectral components having the RHCPcharacteristic polarization state and a wavelength within the bluereflective band Δλ_(B) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The pass-band polarizing reflectiveelement associated with each “blue” subpixel is “tuned” duringfabrication in the manner described hereinabove.

As shown in FIG. 10E, each pass-band polarizing reflective element 10B″associated with a “green” subpixel in the pixelated pass-band circularpolarizing panel 10 is particularly designed to reflect nearly 100% allspectral components having the RHCP characteristic polarization stateand wavelengths within the red reflective band Δλ_(R) and the bluereflective band Δλ_(B), whereas all spectral components having the RHCPcharacteristic polarization state and a wavelength within the greenreflective band Δλ_(G) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The pass-band polarizing reflectiveelement associated with each “green” subpixel is “tuned” duringfabrication in the manner described hereinabove.

As shown in FIG. 10F, each pass-band polarizing reflective element 10A″associated with a “red” subpixel in the pixelated pass-band circularpolarizing panel 10 is particularly designed to reflect nearly 100% allspectral components having the RHCP characteristic polarization stateand wavelengths within the green reflective band Δλ_(G) and the bluereflective band Δλ_(B), whereas all spectral components having the RHCPcharacteristic polarization state and a wavelength within the redreflective band Δλ_(R) are transmitted nearly 100% through the pass-bandpolarizing reflective element. The pass-band polarizing reflectiveelement associated with each “red” subpixel is “tuned” duringfabrication in the manner described hereinabove.

The preferred method of making broad-band circular polarizing reflectivepanels 8″ and 11″ shown in FIGS. 10A1 and 10A2 is disclosed in U.S.Letters Patent No. 5,691,789, entitled “Single Layer Reflective SuperBroadband Circular Polarizer and Method of Fabrication Therefor”, supra.The pixelated pass-band circularly polarizing reflective panel 10″ canbe fabricated in a manner similar to the way described in LCD panelfabrication method described in detail hereinabove.

Operation Of The First And Second Illustrative Embodiments of the LCDPanel of the Second Generalized Embodiment of the Present Invention

Having described in detail how to make the LCD panels illustrated inFIGS. 8, 9A1, 9A2, and 10A1 and 10A2, it is appropriate at this junctureto now describe their operation with reference to the exemplary pixelstructure detailed in such figure drawings.

As shown in FIGS. 9A1 and 9A2, unpolarized light is produced within thebacklighting structure and is composed of spectral components havingboth LP1 and LP2 polarization states. Only spectral components havingthe LP2 polarization state are transmitted through the broad-band linearpolarizing reflective panel 8′ adjacent the backlighting panel 7,whereas spectral components having polarization state LP1 incidentthereon are reflected therefrom without energy loss or absorption.Spectral components reflecting off broad-band linear polarizingreflective panel 8′ on the backlighting structure side strikequasi-diffusive reflector 7A, and undergo a polarization inversion (i.e.LP1 to LP2 and LP2 to LP1). This reflection process occurs independentof wavelength. The spectral components having the LP2 polarization stateare retransmitted through the broad-band linear polarizing reflectivepanel 8′ adjacent the backlighting structure.

When a linear polarization rotating element 9A′, 9B′, 9C′ is controlledin its inactive-state as shown in FIG. 9A1, the linear polarizationrotating element will transmit the spectral components therethroughindependent of wavelength while effecting a conversion in polarizationstate (i.e. LP1 to LP2 and LP2 to LP1), thereby producing a “bright”subpixel level in response to the inactive-state into which it has beendriven.

When a “red” subpixel is driven into its “bright” state as shown in FIG.9A1, spectral components within the backlighting structure havingwavelengths within the “red” band Δλ_(R) and a polarization state LP2(i.e. λ_(R) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the “red” pass-band linearly polarizingreflective element 10A′, the linear polarization direction rotatingelement 9A′ and the broad-band linearly polarizing reflective panel 11′without absorption. In this state, spectral components within thebacklighting structure having wavelengths within the “green” band Δλ_(G)and “blue” band Δλ_(B) and a polarization state LP2 (i.e. λ_(G) ^(LP2)λ_(B) ^(LP2)) are transmitted through the broad-band linear polarizingreflective panel 8′ and are reflected off the “red” pass-band linearlypolarizing reflective element 10A′ and retransmitted through broad-bandlinear polarizing reflective panel 8′ back into the backlightingstructure for systemic recycling.

When a “green” subpixel is driven into its “bright” state as shown inFIG. 9A1, spectral components within the backlighting structure havingwavelengths within the “green” band Δλ_(G) and a polarization state LP2(i.e. λ_(G) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the “green” pass-band linearlypolarizing reflective element 10B′, the linear polarization directionrotating element 9B′ and the broad-band linearly polarizing reflectivepanel 11′ without absorption. In this state, spectral components withinthe backlighting structure having wavelengths within the “red” bandΔλ_(R) and “blue” band Δλ_(B) and a polarization state LP2 (i.e. λ_(R)^(LP2) λ_(B) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′ and reflected off the “green” pass-bandlinearly polarizing reflective element 10B′ and retransmitted throughbroad-band linear polarizing reflective panel 8′ back into thebacklighting structure for systemic recycling.

When a “blue” subpixel is driven into its “bright” state as shown inFIG. 10A1, spectral components within the backlighting structure havingwavelengths within the “blue” band Δλ_(B) and a polarization state LP2(i.e. λ_(B) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the “blue” pass-band linearly polarizingreflective element 10C′, the linear polarization direction rotatingelement 9C′ and the broad-band linearly polarizing reflective panel 11′without absorption. In this state, spectral components within thebacklighting structure having wavelengths within the “red” band Δλ_(R)and “green” band Δλ_(G) and a polarization state LP2 (i.e. λ_(R) ^(LP2)λ_(G) ^(LP2)) are transmitted through the broad-band linear polarizingreflective panel 8′ and reflected off the “blue” pass-band linearlypolarizing reflective element 10C′ and retransmitted through thebroad-band linearly polarizing reflective panel 8′ back into thebacklighting structure for systemic recycling.

When a linear polarization rotating element associated with a red, greenor blue subpixel is driven into its active-state as shown in FIG. 9A2,the linear polarization rotating element associated therewith willtransmit the spectral components therethrough independent of wavelengthwithout effecting an orthogonal conversion in polarization state (i.e.LP1 to LP1 or LP2 to LP2), thereby producing a “dark” subpixel level inresponse to the active-state into which it has been driven.

When a “red” subpixel is driven into its “dark” state shown in FIG. 9A2,spectral components within the backlighting structure having wavelengthswithin the “red” band Δλ_(R) and polarization state LP2 (i.e. λ_(R)^(LP2)) are transmitted through the broad-band linear polarizingreflective panel 8′, the “red” pass-band linearly polarizing reflectiveelement 10A′ and linear polarization direction rotating element 9A′ andreflect off broad-band linearly polarizing reflective panel 11′ withoutabsorption. The reflected “red” spectral components with the LP2polarization state (i.e. λ_(R) ^(LP2)) are then retransmitted throughthe linear polarization direction rotating element 9A′, the pass-bandlinearly polarizing reflective element 10A′, and the broad-band linearlypolarizing reflective panel 8″ back into the backlighting structure forrecycling among neighboring subpixels. At the same time, spectralcomponents having wavelengths within the “green” band Δλ_(G) or “blue”band Δλ_(B) and polarization state LP2 (i.e. λ_(G) ^(LP2), λ_(B) ^(LP2))are transmitted through broad-band linearly polarizing reflective panel8′ and reflected off the “red” pass-band polarizing reflective element10A′ and then retransmitted through the broad-band linearly polarizingreflective panel 8′ back into the backlighting structure for recyclingamong neighboring subpixels.

When a “green” subpixel is driven into its “dark” state shown in FIG.9A2, spectral components within the backlighting structure havingwavelengths within the “green” band Δλ_(G) and polarization state LP2(i.e. λ_(G) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the “green” pass-band linearlypolarizing reflective element 10B′ and linear polarization directionrotating element 9B′ and reflect off broad-band linearly polarizingreflective panel 11′ without absorption. The reflected “green” spectralcomponents with the LP2 polarization state (i.e. λ_(G) ^(LP2)) are thenretransmitted through the linear polarization direction rotating element9B′ (without polarization rotation), the pass-band linearly polarizingreflective element 10B′, and the broad-band linearly polarizingreflective panel 8′ back into the backlighting structure for recyclingamong neighboring subpixels. At the same time, spectral componentshaving wavelengths within the “red” band Δλ_(R) or “blue” band Δλ_(B)and polarization state LP2 (i.e. λ_(R) ^(LP2), λ_(B) ^(LP2)) aretransmitted through broad-band polarizing reflective panel 8′ andreflected off the “green” pass-band polarizing reflective element 10B′,and then retransmitted through the broad-band linearly polarizingreflective panel 8′ back into the backlighting structure for recyclingamong neighboring subpixels.

When a “blue” subpixel is driven into its “dark” state shown in FIG.9A2, spectral components within the backlighting structure havingwavelengths within the “blue” band Δλ_(B) and polarization state LP2(i.e. λ_(B) ^(LP2)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the “blue” pass-band linearly polarizingreflective element 10C′ and linear polarization direction rotatingelement 9C′ and reflect off the broad-band linearly polarizingreflective panel 11′ without absorption. The reflected “blue” spectralcomponents with the LP2 polarization state (i.e. λ_(B) ^(LP2)) are thenretransmitted through the linear polarization direction rotating element9C′ (without polarization rotation), the pass-band linearly polarizingreflective element 10C′, and the broad-band linearly polarizingreflective panel 8′ back into the backlighting structure for recyclingamong neighboring subpixels. At the same time, spectral componentswithin the backlighting structure having wavelengths within the “red”band Δλ_(R) or “green” band Δλ_(G) and polarization state LP2 (i.e.λ_(R) ^(LP2), λ_(G) ^(LP2)) are transmitted through broad-bandpolarizing reflective panel 8′ and reflected off the “blue” pass-bandpolarizing reflective element 10B′ and then retransmitted through thebroad-band linearly polarizing reflective panel 8 back into thebacklighting structure for recycling among neighboring subpixels.

As shown in FIGS. 10A1 and 10A2, unpolarized light is produced withinthe backlighting structure and is composed of spectral components havingboth LHCP and RHCP polarization states. Only spectral components withinthe backlighting structure having the RHCP polarization state aretransmitted through the broad-band circularly polarizing reflectivepanel 8″ adjacent the backlighting structure 7, whereas spectralcomponents therewithin having polarization state LHCP incident thereonare reflected therefrom without energy loss or absorption. Spectralcomponents reflecting off broad-band circularly polarizing reflectivepanel 8″ on the backlighting structure side strike quasi-diffusivereflector 7A and undergo a polarization inversion (i.e. LHCP to RHCP andRHCP to LHCP). This reflection process occurs independent of wavelength.Only spectral components having the RHCP polarization state areretransmitted through the broad-band circularly polarizing reflectivepanel along the projection axis of the LCD panel.

When a circular polarization rotating element associated with a red,green or blue subpixel is driven into its active-state as shown in FIG.10A1, the circular polarization rotating element associated therewithtransmits the spectral components therethrough independent of wavelengthwhile effecting an orthogonal conversion in polarization state (i.e.LHCP to RHCP and RHCP to LHCP), thereby producing a “bright” subpixellevel in response to the active-state into which it has been driven.

When a “red” subpixel is driven into its “bright” state shown in FIG.10A1, spectral components within the backlighting structure havingwavelengths within the “red” band Δλ_(R) and polarization state RHCP(i.e. λ_(R) ^(RHCP)) are transmitted through the broad-band linearpolarizing reflective panel 8″, the “red” pass-band circularlypolarizing reflective element 10A″, the circular polarization directionrotating element 9A″, and the broad-band circularly polarizingreflective panel 11″ without absorption. The “green” and “blue” spectralcomponents with the RHCP polarization state (i.e. λ_(G) ^(RHCP), λ_(B)^(RHCP)) are transmitted through the broad-band linear polarizingreflective panel 8′ and reflected off the “red” pass-band circularlypolarizing reflective element 10A″, and are retransmitted through thebroad-band circularly polarizing reflective panel 8″ back into thebacklighting structure for recycling among neighboring subpixels.

When a “green” subpixel is driven into its “bright” state shown in FIG.10A1, spectral components having wavelengths within the “green” bandΔλ_(G) and polarization state RHCP (i.e. λ_(G) ^(RHCP)) are transmittedthrough the broad-band linear polarizing reflective panel 8′, the“green” pass-band circularly polarizing reflective element 10B″, thecircular polarization direction rotating element 9B″, and the broad-bandcircularly polarizing reflective panel 11″ without absorption. The “red”and “blue” spectral components with the RHCP polarization state (i.e.λ_(R) ^(RHCP), λ_(B) ^(RHCP)) are transmitted through the broad-bandlinear polarizing reflective panel 8′ and reflected off the “green”pass-band circularly polarizing reflective element 10B″, and areretransmitted through the broad-band circularly polarizing reflectivepanel 8″ back into the backlighting structure for recycling amongneighboring subpixels.

When a “blue” subpixel is driven into its “bright” state shown in FIG.10A1, spectral components within the backlighting structure havingwavelengths within the “blue” band Δλ_(B) and polarization state RHCP(i.e. λ_(B) ^(RHCP)) are transmitted through the broad-band linearpolarizing reflective panel 8′, the “blue” pass-band circularlypolarizing reflective element 10C″, the circular polarization directionrotating element 9C″, and the broad-band circularly polarizingreflective panel 11″ without absorption. The “red” and “green” spectralcomponents with the RHCP polarization state (i.e. λ_(R) ^(RHCP), λ_(G)^(RHCP)) are transmitted through the broad-band linear polarizingreflective panel 8′ and reflected off the “blue” pass-band circularlypolarizing reflective element 10C″, and are retransmitted through thebroad-band circularly polarizing reflective panel 8″ back into thebacklighting structure for recycling among neighboring subpixels.

When a circular polarization rotating element is controlled in itsinactive-state as shown in FIG. 10A2, the polarization rotating elementtransmits the spectral components therethrough independent of wavelengthwithout effecting a conversion in polarization state, thereby producinga “dark” subpixel level.

When a “red” subpixel is driven into its “dark” state as shown in FIG.10A2, spectral components within the backlighting structure havingwavelengths within the “red” band Δλ_(R) and a polarization state RHCP(i.e. λ_(R) ^(RHCP)) are transmitted through the broad-band circularlypolarizing reflective panel 8″, the “red” pass-band circularlypolarizing reflective element 10A″ and the circular polarizationrotating element 9A″ and reflected off the broad-band circularlypolarizing reflective panel 11″ without absorption. In this state, thesereflected spectral components are then retransmitted through thecircular polarization rotating element 9A″, the “red” pass-band circularpolarizing reflective element 10A″ and the broad-band circularlypolarizing reflective panel 8″ back into the backlighting structure forrecycling among the neighboring subpixels. Spectral components withinthe backlighting structure having wavelengths within the “green” bandΔλ_(G) or “blue” band Δλ_(B) and a polarization state RHCP (i.e. λ_(G)^(RHCP) λ_(B) ^(RHCP)) are transmitted through the broad-band circularlypolarizing reflective panel 8″ and are reflected off the “red” pass-bandcircularly polarizing reflective element 10A″ and retransmitted throughthe broad-band circularly polarizing reflective panel 8″ back into thebacklighting structure for recycling among neighboring subpixels.

When a “green” subpixel is driven into its “dark” state as shown in FIG.10A2, spectral components within the backlighting structure havingwavelengths within the “green” band Δλ_(G) and a polarization state RHCP(i.e. λ_(G) ^(RHCP)) are transmitted through the broad-band circularlypolarizing reflective panel 8″, the “green” pass-band circularlypolarizing reflective element 10B″, and the circular polarizationrotating element 9B″ and reflected off the broad-band circularlypolarizing reflective panel 11″ without absorption. In this state, thesereflected spectral components are then retransmitted through thecircular polarization rotating element 9B″, the “green” pass-bandcircular polarizing reflective element 10B″ and the broad-bandcircularly polarizing reflective panel 8″ back into the backlightingstructure for recycling among the neighboring subpixels. Spectralcomponents within the backlighting structure having wavelengths withinthe “red” band Δλ_(R) or “blue” band Δλ_(B) and a polarization stateRHCP (i.e. λ_(R) ^(RHCP), λ_(B) ^(RHCP)) are transmitted through thebroad-band circularly polarizing reflective panel 8″ and are reflectedoff the “green” pass-band circularly polarizing reflective element 10B″and retransmitted through the broad-band circularly polarizingreflective panel 8″ back into the backlighting structure for recyclingamong neighboring subpixels.

When a “blue” subpixel is driven into its “dark” state as shown in FIG.10A2, spectral components within the backlighting structure havingwavelengths within the “blue” band Δλ_(B) and a polarization state RHCP(i.e. λ_(B) ^(RHCP)) are transmitted through the broad-band circularlypolarizing reflective panel 8″, the “blue” pass-band circularlypolarizing reflective element 10C″, and the circular polarizationrotating element 9C″ and reflected off the broad-band circularlypolarizing reflective panel 11″ without absorption. In this state, thesereflected spectral components are then retransmitted through thecircular polarization rotating element 9C″, the “blue” pass-bandcircular polarizing reflective element 10C″ and the broad-bandcircularly polarizing reflective panel 8″ back into the backlightingstructure for recycling among the neighboring subpixels. Spectralcomponents within the backlighting structure having wavelengths withinthe “red” band Δλ_(R) or “green” band Δλ_(G) and a polarization stateRHCP (i.e. λ_(R) ^(RHCP), λ_(G) ^(RHCP)) are transmitted through thebroad-band circularly polarizing reflective panel 8″ and are reflectedoff the “blue” pass-band circularly polarizing reflective element 10C″and retransmitted through the broad-band circularly polarizingreflective panel 8″ back into the backlighting structure for recyclingamong neighboring subpixels.

Alternative Embodiments of the LCD Panel Hereof

Expectedly, the extinction ratio for the broad-band linear polarizingreflective panels employed in the LCD panels of FIGS. 2 and 8 may beless than optimum. Consequently, a small percentage of incident lightenergy passing through the LCD panel will be imparted with theorthogonal polarization state and will be perceived by the viewer asspatial noise, degrading the image contrast attainable by the displaysystem.

Surprisingly, it has been discovered that it is possible to markedlyimprove the contrast of image displayed from the LCD panels hereof byemploying energy absorbing polarizers within the LCD panel constructionin a way which absorbs orthogonal “noise” components produced by thebroad-band polarizing “reflective” panels employed therein, withouteffecting the light recycling mechanisms carried out at the variousstages of the LCD panel. As will be described in greater detail below,this technique involves mounting to each broad-band polarizingreflective panel, an absorptive-type broad-band polarizing filter havinga polarization state that is “matched” to the polarization state of itscorresponding broad-band polarizing reflective panel. Modified versionsof the four illustrative LCD panel embodiments hereof are shown in FIGS.11 through 14.

In FIG. 11, the LCD panel of FIGS. 3A1 and 3A2 is shown modified bymounting a first broad-band absorptive linear polarizer 8A′ to the frontsurface of broad-band polarizing reflective panel 8′, and mounting asecond broad-band absorptive linear polarizer 11A′ to the front surfaceof broad-band polarizing reflective panel 11′. The polarization state ofbroad-band absorptive linear polarizer 8′ is LP1 in order to match theLP1 polarization state of broad-band polarizing reflective panel 8′.Such polarization matching ensures that spectral energy which is notreflected from the broad-band polarizing reflective panel 8′, but istransmitted (i.e. leaked) therethrough due to a suboptimal extinctionratio, is absorbed by the broad-band absorptive linear polarizer 8A′through energy dissipation. Similarly, the polarization state ofbroad-band absorptive linear polarizer 1IA′ is LP1 in order to match theLP1 polarization state of broad-band polarizing reflective panel 11′.Such polarization matching ensures that spectral energy which is notreflected from the broad-band polarizing reflective panel 11′, but istransmitted (i.e. leaked) therethrough due to a suboptimal extinctionratio, is absorbed by the broad-band absorptive linear polarizer 11A′through energy dissipation. The use of broad-band absorptive linearpolarizers 8A′ and 11A′ substantially improves the contrast of imagesformed by the LCD panel, without reducing the light transmissionefficiency along the light projection axis of the LCD panel which, asshown in FIG. 2, extends from the backlighting structure towards theeyes of the viewer. Such broad-band absorptive polarizers can berealized using dichroic polarizing material well known in the art.Preferably, these absorptive polarizing filter panels 8A′ and 11A′ arelaminated directly onto broad-band polarizing reflective panels 8′ and11′, respectively, during the fabrication process of the LCD panel.

In FIG. 12, the LCD panel of FIGS. 4A1 and 4A2 is shown modified bymounting a first broad-band absorptive circular polarizer 8A″ to thefront surface of broad-band circularly polarizing reflective panel 8″,and mounting a second broad-band absorptive circular polarizer 11A″ tothe front surface of broad-band circularly polarizing reflective panel11″. The polarization state of broad-band absorptive circular polarizer8A″ is LHCP in order to match the LHCP polarization state of broad-bandcircularly polarizing reflective panel 8″. Such polarization matchingensures that spectral energy which is not reflected from the broad-bandpolarizing reflective panel 8″, but is transmitted (i.e. leaked)therethrough due to a suboptimal extinction ratio, is absorbed by thebroad-band absorptive circular polarizer 8A″ through energy dissipation.Similarly, the polarization state of broad-band absorptive circularpolarizer 11′A″ is RHCP in order to match the RHCP polarization state ofbroad-band polarizing reflective panel 11″. Such polarization matchingensures that spectral energy which is not reflected from the broad-bandpolarizing reflective panel 11″, but is transmitted (i.e. leaked)therethrough due to a suboptimal extinction ratio, is absorbed by thebroad-band absorptive circular polarizer 11″ through energy dissipation.The use of broad-band absorptive circular polarizers 8A″ and 11A″substantially improves the contrast of images formed by the LCD panel,without reducing the light transmission efficiency along the lightprojection axis of the LCD panel. Such broad-band absorptive polarizerscan be realized using dichroic polarizing material well known in theart. Preferably, these absorptive circularly polarizing filter panels8A″ and 11″ are laminated directly onto broad-band circularly polarizingreflective panels 8″ and 11″, respectively, during the fabricationprocess of the LCD panel.

In FIG. 13, the LCD panel of FIGS. 9A1 and 9A2 is shown modified bymounting a first broad-band absorptive linear polarizer 8A′ to the frontsurface of broad-band polarizing reflective panel 8′, and mounting asecond broad-band absorptive linear polarizer 11A′ to the front surfaceof broad-band polarizing reflective panel 11′. The polarization state ofbroad-band absorptive linear polarizer 8A′ is LP1 in order to match theLP1 polarization state of broad-band polarizing reflective panel 8′.Such polarization matching ensures that spectral energy which is notreflected from the broad-band polarizing reflective panel 8′, but istransmitted (i.e. leaked) therethrough due to a suboptimal extinctionratio, is absorbed by the broad-band absorptive linear polarizer 8A′through energy dissipation. Similarly, the polarization state ofbroad-band absorptive linear polarizer 11A′ is LP2 in order to match theLP2 polarization state of broad-band polarizing reflective panel 11′.Such polarization matching ensures that spectral energy which is notreflected from the broad-band polarizing reflective panel 11′, but istransmitted (i.e. leaked) therethrough due to a suboptimal extinctionratio, is absorbed by the broad-band absorptive linear polarizer 11A′through energy dissipation. Preferably, these absorptive polarizingfilter panels 8A′ and 11A′ are laminated directly onto broad-bandpolarizing reflective panels 8 and 11, respectively. The use ofbroad-band absorptive linear polarizers 8A′ and 8A″ substantiallyimproves the contrast of images formed by the LCD panel, withoutreducing the light transmission efficiency along the light projectionaxis of the LCD panel. Such broad-band absorptive polarizers can berealized using dichroic polarizing material well known in the art.

In FIG. 14, the LCD panel of FIGS. 10A1 and 10A2 is shown modified bymounting a first broad-band absorptive circular polarizer 8A″ to thefront surface of broad-band circularly polarizing reflective panel 8″,and mounting a second broad-band absorptive circular polarizer 11″ tothe front surface of broad-band circularly polarizing reflective panel11″. The polarization state of broad-band absorptive circular polarizer8A″ is LHCP in order to match the LHCP polarization state of broad-bandcircularly polarizing reflective panel 8″. Such polarization matchingensures that spectral energy which is not reflected from the broad-bandpolarizing reflective panel 8″, but is transmitted (i.e. leaked)therethrough due to a suboptimal extinction ratio, is absorbed by thebroad-band absorptive circular polarizer 8A″ through energy dissipation.Similarly, the polarization state of broad-band absorptive circularpolarizer 11″ is RHCP in order to match the RHCP polarization state ofbroad-band polarizing reflective panel 11″. Such polarization matchingensures that spectral energy which is not reflected from the broad-bandpolarizing reflective panel 11″, but is transmitted (i.e. leaked)therethrough due to a suboptimal extinction ratio, is absorbed by thebroad-band absorptive circular polarizer 11A″ through energydissipation. Preferably, these absorptive circularly polarizing filterpanels 8A″ and 11A″ are laminated directly onto broad-band circularlypolarizing reflective panels 8″ and 11″, respectively. The use ofbroad-band absorptive circular polarizers 8A″ and 11″ substantiallyimproves the contrast of images formed by the LCD panel, withoutreducing the light transmission efficiency along the light projectionaxis of the LCD panel. Such broad-band absorptive polarizers can berealized using dichroic polarizing material well known in the art.

In general, there are many applications to which the LCD panels of thepresent invention can be put. One such application is illustrated inFIG. 15. As shown, the LCD panel hereof cane be integrated into aultra-high brightness color image projection system of transportabledesign. In this particular embodiment, the image projection system isembodied within a laptop computer system having both direct andprojection viewing modes, similar to the systems described inApplicant's: U.S. Letters Pat. No. 5,860,233 entitled “IMAGE DISPLAYSYSTEMS HAVING DIRECT AND PROJECTION VIEWING MODES”; U.S. Letters PatentNo. 5,801,793 entitled “BACKLIGHTING CONSTRUCTION FOR USE INCOMPUTER-BASED DISPLAY SYSTEMS HAVING DIRECT AND PROJECTION VIEWINGMODES OF OPERATION” and U.S. Letters Pat. No. 5,828,427 entitled“ELECTO-OPTICAL BACKLIGHTING PANEL FOR USE IN COMPUTER-BASED DISPLAYSYSTEMS AND PORTABLE LIGHT PROJECTION DEVICE FOR USE THEREWITH”.

An Illustrative Application of LCD Panel of the Present Invention

As shown in FIG. 15, portable image projection system 30 comprises anumber of subsystem components, namely: a compact housing oftransportable construction having a display portion 31A with afrontwardly located display window 32, and a base portion 32B hingedlyconnected to the display portion 31A and having a keypad 33 and apointing device 34; an LCD panel 2, 2′ according to the presentinvention described above, mounted within the housing display portion31A; an ultra-thin projection lens panel 35 (e.g. Fresnel lens,holographic lens, etc.) laminated to the front surface of the LCD panel2; a backlighting structure 7′ of cascaded construction, mounted to therear of the LCD panel 2 in a conventional manner; associated apparatus36, (e.g. pixel driver circuitry, image display buffers, an imagedisplay controller, a rechargeable battery power supply, input/outputcircuitry for receiving video input signals from various types ofexternal sources, microprocessor and associated memory, etc.), containedwithin the base portion 31B; a projection lens 37 supported by a bracket38 which can be removed during the direct viewing mode and stored withina compartment 39 formed within the base portion of the housing; and anelectro-optically controllable light diffusing panel 40 which does notscatter backprojected light in the projection viewing mode, and scattersback project light in the direct viewing mode.

In the direct-viewing mode of the system of FIG. 15, the projection lens38 is stored within compartment 39, electro-optically controllable lightdiffusing panel 40 is switched to its light scattering state, and thebacklighting structure produces light which is spatial-intensitymodulated and spectrally filtered to produce color images on the surfaceof the LCD panel 2. In the projection-viewing mode, the projection lens38 is mounted along the projection axis (optical axis) 41 of the Fresnellens panel 35, electro-optically controllable light diffusing panel 40is switched to its light non-scattering state, and the backlightingstructure produces light which is spatial-intensity modulated andspectrally filtered to produce color images on the surface of the LCDpanel 2. Projection lens 37 projects the formed color image onto aremote viewing surface 42 for projection viewing. By virtue of theultra-high light transmission efficiency of the LCD panel 2 hereof, thesystem of FIG. 15 can projected bright color images onto remote surfaceswithout the use of external high-intensity lighting sources required byprior art LCD projection systems. In portable applications, such imagescan be projected using the battery power source aboard the transportablesystem. With this design, there is not need for a rearwardly openingwindow in the back of display housing portion 31A, required of prior artprojection system. When not in use, the system easily folds into aultra-slim book-like configuration for easy of storage andtransportability.

Modifications

Having described in the illustrative embodiments of the presentinvention, several modifications readily come to mind.

In each illustrative embodiment of the LCD panel hereof, the light“reflecting” properties of the subpixel spectral filter elements 10A,10B, 10C have been realized using the polarization-reflective propertiesof CLC materials. It is understood, however, that these subcomponents ofthe LCD panel of the present invention may be realized using otherenabling technologies, such as: (i) holographic reflective filtertechnology of the type disclosed in “Holographic Color Filters for LCDs”by John Biles, published in SID 94 DIGEST, pages 403-406; and/or (ii)thin-film optical interference filter technology of the type disclosedin “Design Issues in Using Thin-Film Optical Interference Filters asColor Filters for LCD System Applications” by S-F. Chen and H-P D.Shieh, published in SID 94 DIGEST (1994), pages 411-416. In suchalternative embodiments, it would be preferred to employ broad-bandpolarizing reflective panels 8 and 11 having the polarization reflectiveproperties as described hereinabove so that the systemic light recyclingprocess of the present invention is preserved.

The modifications described above are merely exemplary. It is understoodthat other modifications to the illustrative embodiments will readilyoccur to persons with ordinary skill in the art. All such modificationsand variations are deemed to be within the scope and spirit of thepresent invention as defined by the accompanying Claims to Invention.

What is claimed is:
 1. An image display panel employing the recycling oflight from a plurality of light reflective elements therewithin so as toproduce color images with enhanced brightness, said image display panelcomprising: a backlighting structure including a light source forproducing light consisting of spectral components having wavelengthsover a substantial portion of the visible band of said electromagneticspectrum, and a broad-band reflector for reflecting, within saidbacklighting structure, polarized light consisting of spectralcomponents having wavelengths over a substantial portion of said visibleband and, upon one or more reflections within said backlightingstructure, converting the polarization state of said spectral componentsfrom a first polarization state (P1) to a second polarization state (P2)orthogonal to said first polarization state (P1), and from said secondpolarization state (P2) to said first polarization state (P1); aplurality of pixel regions spatially encompassed within a predefinedimage display area definable relative to said backlighting structure,wherein each said pixel region spatially encompasses a plurality ofsubpixel regions and each said subpixel region within each saidspatially-encompassing pixel region has a predefined spectral band overthe visible band of the electromagnetic spectrum; a broad-bandreflective polarizer for reflecting light consisting substantially ofspectral components having wavelengths over a substantial portion ofsaid visible band and said first polarization state (P1), andtransmitting a distribution of polarized light along a prespecifieddirection, substantially confined within said predefined image displayarea, and consisting substantially of spectral components havingwavelengths over a substantial portion of said visible band and saidsecond polarization state (P2); a spatial intensity modulation structureincluding an array of polarization modifying elements, each saidpolarization modifying element being spatially registered with one saidsubpixel region and selectively modifying the polarization state ofpolarized light transmitted therethrough in response to a subpixel drivesignal provided to said polarization modifying element, and a broad-bandpolarizer, cooperating with said array of polarization modifyingelements, so as to modulate the spatial intensity of said produceddistribution of polarized light and thereby produce a dark-type orbright-type intensity level at each said subpixel region along saidbroad-band polarizer; and a spectral filtering structure having apixelated array of pass-band reflective-type spectral filtering elementsrealized within a single layer of optical material, for spectrallyfiltering said polarized light, each said pass-band reflective-typespectral filtering element being spatially registered with one saidsubpixel region and tuned to one said predefined spectral band fortransmitting only the spectral components of said polarized light havingwavelengths within said predefined spectral band of said subpixelregion, and reflecting the spectral components of said producedpolarized light having wavelengths outside said predefined spectral bandof said subpixel region so as to produce a predefined color value atsaid subpixel region spatially-registered with said pass-bandreflective-type spectral filtering element; wherein, the spectralcomponents of polarized light that are transmitted through saidbroad-band reflective polarizer along said prespecified directioncontribute to said distribution of polarized light; wherein, thespectral components of polarized light that are not transmitted throughsaid broad-band reflective polarizer along said prespecified directionare reflected off said broad-band reflective polarizer and transmittedback towards said broad-band reflector for reflection and/orpolarization conversion within said backlighting structure andretransmission through said broad-band reflective polarizer so as tocontribute to said distribution of polarized light; wherein, thespectral components of said polarized light that are transmitted throughthe pass-band reflective-type spectral filtering element at each saidsubpixel region within each said spatially-encompassing pixel regionproduce said predefined color value at said subpixel region; andwherein, the spectral components of said polarized light that are nottransmitted through the pass-band reflective-type spectral filteringelement at each said subpixel region within each saidspatially-encompassing pixel region are reflected off said pass-bandreflective-type spectral filtering element and transmitted back towardssaid backlighting structure for reflection and/or polarizationconversion and retransmission towards the other said subpixel regionswithin said spatially-encompassing pixel region in said spectralfiltering structure; whereby said color images are produced from saidpredefined image display area having enhanced brightness.
 2. The imagedisplay panel of claim 1, wherein said spectral filtering structure isdisposed between said backlighting structure and said spatial intensitymodulation structure.
 3. The image display panel of claim 2, whereinsaid single layer of optical material comprises a single layer of liquidcrystal material.
 4. The image display panel of claim 2, wherein eachsaid polarization modifying element is an optical element made fromliquid crystal material.
 5. The image display panel of claim 2, whereinsaid backlighting structure further comprises a light guiding paneldisposed between said broad-band reflector and said broad-bandreflective polarizer for guiding said produced light over said imagedisplay area.
 6. The image display panel of claim 2, wherein said firstpolarization state is a first linear polarization state and said secondpolarization state is a second linear polarization state orthogonal tosaid first linear polarization state.
 7. The image display panel ofclaim 2, wherein said first polarization state is a first circularpolarization state and said second polarization state is a secondcircular polarization state orthogonal to said first circularpolarization state.
 8. The image display panel of claim 2, saidbroad-band reflector is a quasi-diffusive reflector.
 9. The imagedisplay panel of claim 2, wherein said plurality of subpixel regionswithin each said spatially-encompassing pixel region have colorcharacteristics associated with the RGB (red, green, blue) additiveprimary color system.
 10. The image display panel of claim 1, whereinsaid spatial intensity modulation structure is disposed between saidbacklighting structure and said spectral filtering structure.
 11. Theimage display panel of claim 10, wherein said plurality of subpixelregions within each said spatially-encompassing pixel region have colorcharacteristics associated with the CMY (cyan, magenta, yellow)subtractive primary color system.
 12. The image display panel of claim11, wherein said “red” pass-band transmits spectral components of lightwithin said “red” pass-band and reflects substantially all spectralcomponents of light within said “green” pass-band and said “blue”pass-band, wherein said “green” pass-band transmits spectral componentsof light within said “green” pass-band and reflects substantially allspectral components of light within said “red” pass-band and said “blue”pass-band, and wherein said “blue” pass-band transmits spectralcomponents of light within said “blue” pass-band and reflectssubstantially all spectral components of light within said “red”pass-band and said “green” pass-band.
 13. The image display panel ofclaim 11, wherein said backlighting structure further comprises a lightguiding panel disposed between said broad-band reflector and saidbroad-band reflective polarizing filter for guiding said produced lightover said predefined image display area.
 14. The image display panel ofclaim 10, wherein each said spectral filtering element is an opticalelement made from a material selected from the group consisting ofliquid crystal material, holographic-type material, andinterference-type material.
 15. The image display panel of claim 10,wherein each said polarization modifying element is an optical elementmade from liquid crystal material.
 16. The image display panel of claim10, wherein said first polarization state is a first linear polarizationstate and said second polarization state is a second linear polarizationstate orthogonal to said first linear polarization state.
 17. The imagedisplay panel of claim 10, wherein said first polarization state is afirst circular polarization state and said second polarization state isa second circular polarization state orthogonal to said first circularpolarization state.
 18. The image display panel of claim 10, saidbroad-band polarizing reflector is a quasi-diffusive reflector.
 19. Theimage display panel of claim 1, wherein the spectral components of saidpolarized light producing said bright-type intensity level at eachsubpixel region within said spatially-encompassing pixel region in saidspatial intensity modulation structure are transmitted through saidbroad-band reflective polarizer, and wherein the spectral components ofsaid polarized light not producing said bright-type intensity level arereflected off said broad-band reflective polarizer and transmitted backtowards said backlighting structure for reflection and/or polarizationconversion and retransmission towards the other said subpixel regionswithin said spatially-encompassing pixel region.